Parasitism among the Red AlgæAuthor(s): William Albert SetchellReviewed work(s):Source: Proceedings of the American Philosophical Society, Vol. 57, No. 2 (1918), pp. 155-172Published by: American Philosophical SocietyStable URL: http://www.jstor.org/stable/984166 .Accessed: 06/10/2012 07:15

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PARASITISM AMONG THE RED ALG.E.

By WILLIAM ALBERT SETCHELL.

(Read April 19, 1918)

The question as to when a particular plant is, or is not, a parasite is often difficult to answer, although in many cases the parasitic re-

lation is readily to be inferred because of certain morphological

peculiarities and also because of the apparent dependence of the

one (parasite) upon another (host) in the matter of nourishment.

The fundamental conception is, of course, that the parasite draws

upon the host for materials of greater or less metabolic value,

but, as to amount and extent, is difficult of demonstration and may be inferred largely from various indications of a morphological nature.

There are also to be considered in connection with parasites, especially among the thallophytes, epiphytes and endophytes. A true epiphyte uses the plant upon which it grows only for mechan- ical support. Its metabolism is independent of that of the plant on which it grows. It is conceivable that even those epiphytes which

penetrate the tissues of the supporting plant do so only in a mechan- ical way, although it seems probable that penetration is usually as- sociated with the establishment of metabolic relations.

In case of the endophyte, a variety of relations seems to exist between it and the plant it inhabits. Epiphytes exist both among cormophytes and thallophytes. Endophytes are always thallophytes and they may grow entirely within the body of another plant or only partially so. Some algal endophytes only penetrate between the

layers of the outer walls while others descend deep among the cells of the plants they inhabit. It seems very possible that there may be parasitic relations between many, or most, of the endophytes and their " hosts."

Epiphytes are numerous among the red algae and, while no exact enumeration has been made, it seems safe to say that, at least, half

155

156 SETCHELL?PARASITISM AMONG RED ALG^E.

of the known species are epiphytes. It is very desirable that these

should be investigated as to their relations to the plants on which

they grow. Where epiphytes are constantly observed on a single or

even on a few closely related plants it is to be suspicioned, at least, that there may be some, even if slight, parasitic relation. Polysi- phonia fastigiata (Roth) Grev., e. g., is an epiphyte whose constant occurrence on Ascophyllum nodosum (L.) Le Jolis has been no- ticed. R. J. Harvey Gibson (1891, p. 132) states that "The attach- ment of the epiphyte to Ascophyllum is very intimate" and says farther that " root filaments given off from the base of the frond

penetrate deeply into the tissue of the host and wander amongst the cortical cells and medullary hyphae." A similar penetration of the " host " usually takes place from the base of Pterosiphonia Woodii

(Harv.) Falkenb. into the tissues of the Laminariaceae it grows upon, as observed by N. L. Gardner and myself. Callithamnion

Lejolisea Farlow penetrates deeply into the tissues of the nodes of the Amphiroa on which it is always found. Clara K. Leavitt (1904, p. 294) describes the penetration of Microcladia californica Farlow and also of an unnamed species of Callithamnion into the fronds of "

Callymenia Phyllophora J. Ag." The list will undoubtedly be

considerably extended after carefully examining other " epiphytes."

It remains a question as to whether such forms are to be considered as parasites or not. The Polysiphonia is of low stature, but can

hardly be considered as reduced. The Pterosiphonia and Micro- cladia are often found in very much reduced forms but not as a rule, and they show little, if any, loss of color.

Certain forms of penetration of the plant upon which they ex-

clusively are to be met with occur in the cases of Placophora Binderi J. Ag. and Ceramium codicola J. Ag. Both species grow on Codium and possess rhizoidal filaments which differ from any of the regular outer structures and which penetrate, at least, between the utricles of the Codium. This does not seem to indicate true

parasitism.

Among the marine species of Chantransia (or Acroch?tium) are some epiphytes which are confined to a single

" host " and which are partially, at least, parasites (cf. Rosenvinge, 1909, p. 82). The plants of this genus are all small, whether growing on rock, or

SETCHELL?PARASITISM AMONG RED ALG^E. 157

as true superficial epiphytes, or as wholly or partially endophytes.

Only one of these species has been observed to actually attack the

cells of the host, and that is Chantransia' cytophaga Rosenvinge, growing in the fronds of Porphyra umbilicalis. This species seems

certainly to be reckoned among the parasites. Of endophytes or endozoic species there are a few reds. Be-

sides species of Chantransia or Acroch?tum alluded to above, there are Schmitziella endophl?a Bornet & Batters and Rhodochorton membranaceum Magnus. These are simply within the outer mem-

branes, the former of Cladophora, the latter of Sertularia, one of the Bryozoa. Somewhat more deeply, and also partially, endo-

phytic is Rhodochorton subimmersum Setchell & Gardner, whose main filament is totally included and whose short, erect tetraspo- rangia-bearing branchlets are emersed at their tips. There are sev- eral similar endophytes to be found among the red algae which may be slightly parasitic, but it is difficult to determine this with ex- actness.

In contrast with the various epiphytes and endophytes, such as those mentioned above, are those red algae which seem undoubtedly to be parasites. In placing these among parasites, three criteria of

probable parasitism have been considered, viz., penetration, reduc- tion of thallus and loss of color. It has been considered that at least the first two ought to be present and in very evident form to constitute evidence of parasitism!, while the last may or may not be noticeable.

The undoubted parasite enters the host plant, as a rule, by rhizoidal filaments, or more solid haustoria, which penetrate beyond the superficial assimilating cells into the conducting tissues. It

usually also, establishes more or less conspicuous pit connections be- tween its haustoria and the cells of the host.

The reduction of the thallus or vegetative plant body varies much in the different parasites. As mentioned above, some dwarfing takes place even in certain plants which it seems best to consider, for the time being, at least, as epiphytes, but in those usually reck- oned as parasites, dwarfing is extreme and usually accompanied by a greater or less condensation of the thallus, resulting in tuber- cular growths of greater or less extent. Taken in connection with

158 SETCHELL?PARASITISM AMONG RED ALG.E.

penetration, extreme dwarfing or condensation of the thallus may be

taken to indicate true parasitism of greater or less degree. At the

same time the reproductive organs present little if any metamor-

phosis. In color, parasites vary from little if any loss of pigment to cases

where none is present. Loss of color is always associated with

extreme penetration and very considerable dwarfing or condensation. It is only within the last thirty years that the fact has been

realized that there exists a group of peculiar and undoubted para- sites among the red algae, although a few cases were noted before

that time. Probably the first reference to such a parasite is that by Lyngbye in noting that certain tubercles on " Sph?rococcus Brodi?i"

(Phyllophora Brodi?i) called by him (( Ch?tophora membranifolii"

and which had been considered to be the nemathecia of the plant on which they were found, were no part of the "Sph?rococcus" but belonged to a parasite. This was in 1819 (p. 11, pl. 3, f. B, 3, 4). In 1834 Lyngbye describes this plant in more detail, naming it

Ch?tophora subcutanea (1834, pl. 2135), but saying nothing defi-

nitely as to its being parasitic. Kuetzing, in 1843 (P? I77y pl? 45> f. IV), re-described and named it Actinococcus roseus, seemingly unaware of the earlier description of Lyngbye. The species, which now bears the name Actinococcus subcutaneus (Lyngb.) Rosenvinge, later became the object of a considerable discussion and difference of opinion as to its exact nature (cf. Schmitz, 1893, etc.). It is now recognized as a true parasite by most phycologists.

The second parasite belonging to the red algae to be recognized was Ricardia Montagnei described by Derbes and Solier in 1856 (p. 209, pl. 1 ). This plant, usually assigned to the Bonnemaisoniaceae, forms ovoid red bladders of larger or smaller size, on the tips of

species of Laurencia. Its basal portion occupies the apical pit of the branches of the Laurencia and penetrates into its tissue (cf. Olt-

manns, 1905, p. 326, f. 580). In 1874-75, Reinsch published his " Contributiones ad Algolo-

giam and Fungologiam" and in this he described a number of tu- bercles found on various red algae which be believed to be parasitic members of the same group. Among the tubercles thus described

by Reinsch, some are undoubtedly simply warts or pathologic out-

SETCHELL?PARASITISM AMONG RED ALG^E. 159

growths of the plants on which they are found, but some are un-

doubtedly parasites. Such are some of the plants belonging to his

genera Choreocolax and Syringocolax, but Reinsch did not find any

cystocarps or other organs of frutification on any of his specimens. The work of Reinsch produced little immediate effect and the

basis of truth in it was not recognized until some years had passed. In 1877, however, there appeared the first convincing description and illustration of a parasitic red alga. In this year, Solms Lau- bach published his paper on Janczewskia verruc?formis which pos- sessed all the characteristics convincing of parasitism, viz., deep penetration of the host plant (Laurencia obtusa), reduction of the thallus to a tubercle and color varying from dark red, through orange to pale yellow. In addition to these, it showed cystocarps, antheridia and tetrasporangia. In the case of Janczewskia, as de- scribed by Solms, there can be no doubt either as to the parasitism or as to the nature of the parasite. It is to be noted here also, that the parasite is very closely related to its host and is the first of this sort of parasite to be described among the red algae.

Between the years 1876 and 1889, little was done to further our knowledge of parasitism among the red algae. McNab (1876) re- corded the finding of Choreocolax polysiphoni? Reinsch near Dublin and speaks of its tubercular thallus and penetrating rhizoidal por- tion, but mentions no reproductive organs of any kind. Bornet, in 1878 (pp. 97-99, pl. 50, f. 1-8) described on Jania rubens Lamour a very distinct parasite which he named Melobesia Thureti, noting that it had been described by Harvey as early as 1849 (pl. 201) as a second kind of tetrasporangial conceptacle of Corallina squamata Park. In 1881, Solms Laubach (p. 57, pl. 1, f. 5, pl. 3, f. 12) de- scribed a second parasitic Corallina which he named Melobesia de- formans growing on and in Jania natalensis Harv. and whose apices it distorts through the action of its penetrating rhizoidal filaments. Moebius, also, described a Ceramiaceous parasite on Centroceras clavulatum (Roth.) J. Ag. in 1885 (pp. 77-80, pl. 7), which he named

Episporium centroceratis. The year 1889 may be considered to be the real starting point in

the genuine study of the parasitic red algae. Farlow (1889, p. 6) made known the tetrasporangia of Choreocolax Polysiphoni?

160 SETCHELL?PARASITISM AMONG RED ALGiE.

Reinsch. Schmitz and Reinke (cf. Reinke, 1889, p. 28) described

Harvey ella mirabilis (Reinsch) Schmitz et Reinke (Choreocolax mirabilis Reinsch) with its antheridia and cystocarps, and finally Schmitz, in his "

Systematische Uebersicht der bisher bekannten

Gattungen der Florideen," enumerated eight distinct genera of para- sitic red algae, viz., Actinococcus Kuetzing, Ricardia Derbes et Solier, Choreocolax and Syringocolax Reinsch, Janczewskia Solms, Epi- sporium Moebius, Harveyella Schmitz et Reinke and Choreonema

Schmitz. The last genus was created to contain the Melobesia Thureti Bornet.

The enumeration of Schmitz, together with the discovery of

tetrasporangia, antheridia and cystocarps in Janczewskia and in Epi- sporium, the antheridia and cystocarps in Harveyella, the cystocarps and tetrasporangia in Choreonema, and the tetrasporangia in Choreo- colax were convincing as to the existence of real parasites and led to search for more. In 1891, Richards described the cystocarps as well as the tetrasporangia of Choreocolax Polysiphoni? Reinsch. In 1892 Batters made known Gonimophyllum Buffhami with its cystocarps and tetrasporangia. In 1892, Schmitz published a discussion of the tubercular growths on various red algae, with a view to distinguish- ing those which are true parasites from those which are merely warts or galls. In 1893 Heydrich created the genus Pleurostich-

idium, a Rhodomelaceous genus parasitic on one of the Fucaceae

(Fucodium) in New Zealand. It is dwarf, penetrating and pro- vided with antheridia, cystocarps and tetrasporangia. In the same

year, Schmitz published his very memorable paper on Actinococcus. After a full discussion, Schmitz distinguished between Actinococcus and the true nemathecia of Phyllophora and enumerated four species of Actinococcus besides two for Colacolepis and two for Sterrocolax. He also considered the placing of these genera, deciding upon the

Gigartinaceae, the same family to which the hosts belong, rather than the Squamariaceae, where Actinococcus had previously been as-

signed by J. G. Agardh. The Actinococcus paper of Schmitz provoked considerable dis-

cussion. Darbishire (1894) who had been investigating the species of Phyllophora very carefully, held that the so-called Actinococcus

species were the true nemathecia of Phyllophora and repeated this in

SETCHELL?PARASITISM AMONG RED ALGM. 161

1895. Later, in. 1899, however, Darbishire, after the death of

Schmitz in 1894, published the results of further investigation which resulted in finding the germinating stages of Actinococcus

in the antheridial cavities of the Phyllophora and came to the same

point of view as Schmitz. This point of view was also confirmed

by the investigations of Gomont (1894). In 1894 Kuckuck described the tetrasporangial plant of Harvey-

ella mirabilis (Reinsch) Schmitz et Reinke, under the name of Choreocolax albus, and in 1895 Batters published the genus Callo- colax of Schmitz, a genus whose single species is parasitic on Callo-

phyllis, which is very closely related to itself. In 1896-97 appeared those parts of Engler and Prantl's

" Natuerlichen Pflanzenfamilien " dealing with the red algae and

with whose preparation Schmitz had long been busy. The genera of parasitic red algae were worked over either by Schmitz himself, or by Hauptfleisch or, in case of the Rhodomelaceae, by either Schmitz or Falkenberg. The total number of genera of parasitic red algae was increased from the eight detailed in 1889 to nineteen, the five genera proposed as new in this work belonging entirely to the Rhodomelaceae and parasitic on other members of the same

family. Since 1897, additions have been made to the list of both genera

and species of parasitic red algae. One genus already proposed, viz., Callocolax, was not included in the Engler and Prantl account. This makes twenty genera known up to the close of 1897. Rosen- vinge added Ceratocolax in 1898 (p. 34) and in the same year Foslie (1898, p. 7) created the genus Ch?tolithon to receive the Melobesia d?formons Solms. Falkenberg (1901) in his monograph of the Rhodomelaceae, published more detailed descriptions and figures of the various parasitic genera of this family previously proposed by Schmitz and by himself, but added no new genera. In 1905, Setchell and Lawson (cf. Setchell, 1905, p. 7) proposed the genus Peyssonneliopsis and in 1910 Setchell and Wilson) cf. Wilson, 1910, p. 81) proposed the genus Gracilariophila, which from their point of view is a Gracilaria-like genus parasitic on a Gracilaria (cf. how- ever Eddelb?ttel, 1910, p. 230, 231, and Svedelius, 1911, p. 220-). In 1913, Yendo (p. 283) described and figured a most interesting

162 SETCHELL?PARASITISM AMONG RED ALGiE.

new genus of parasitic red algae belonging to the Rhodomelaceae, which he named Benzaitenia. The single species is parasitic on

other Rhodomelaceae. Finally, M. A. Howe (1914, p. 90) has made

known the genus Lobocolax, which he refers doubtfully to the " Nemalionaceae "

(Helminthocladiaceae Auctt). The single species forms tubercles on Prionitis decipiens (Mont.) J. Ag.

To summarize the genera thus far proposed of parasitic red

algae, there were nineteen recorded by Schmitz and Falkenberg in

1897, an(l six have been proposed since that time. In addition, it

may be stated that there are four additional genera as yet unde- scribed in the collections of the writer. The total number of genera known to the writer, therefore, amounts to twenty-nine. These are all reduced or condensed as to the thallus, penetrating and appar- ently forming protoplasmic connections with the host plants and

varying from full deep red to pure shining white. In regard to species, the number assigned thus far to these genera

and fairly certain, number about fifty and it seems best to give a list of these arranged by families and to indicate in connection with each its host or hosts, in order that the basis for further discussion

may be made clear. In this list there have been included only those

species which seem fairly certain as representing definite and distinct

parasites. All decidedly doubtful species are omitted. An * is

placed against those species which are credited to hosts among the red algae but not of the same family as the parasite and a f against those parasitic on Phaeophyceae. The rest are parasitic on red algae of the same family as themselves.

Helminthocladiaceae.

*i. Lobocolax d?formons Howe (1914), on Prionitis decipiens Mont. J. Ag.

Gelidiace^:.

*2. Choreocolax polysiphoni? Reinsch (1874-75), on Polysiphonia fastigiata (Roth) Grev.

*3. Choreocolax tumidus Reinsch (1874-75), on Ceramium and

Cystoclonium purpuracens (Huds.) Kuetz.

*4. Choreocolax cystoclonii Kylin (1907), on Cystoclonium pur- purase ens (Huds.) Kuetz.

SETCHELL?PARASITISM AMONG RED ALG^E. 163

*5. Harveyella mirabilis (Reinsch) Schmitz et Reinke (1889), on

Rhodomela.

*6. Harveyella pachyderma (Reinsch) Batters (1902), on Graci-

laria confervoides (L.) Grev.

Gigartinace^e.

7. Actinococcus subcutaneus (Lyngb.) Rosenvinge (1893), on

Phyllophora Brodi?i (Turn.) J. Ag. and P. interrupta

(Grev.) J. Ag. 8. Actinococcus aggregatus Schmitz (1893), on Gymnogongrus

Griffithsi? (Turn.) Mart.

9. Actinococcus pelt?formis Schmitz (1893) on Gymnogongrus norv?giens (Gunn.) J. Ag. and G. crenulatus (Turn.) J. Ag.

10. Actinococcus latior Schmitz (1893), on Gymnogongrus dilata- tus (Turn.) J. Ag.

11. Actinococcus mollis M. A. Howe (1914), on Gymnogongrus disciplinalis (Turn.) J. Ag.

12. Actinococcus Chiton M. A. Howe (1914), on Gymnogongrus linearis (Turn.) J. Ag.

13. Colacolepis decipiens Schmitz (1893), on Phyllophora Heredia

(Clem.) J. Ag. 14. Colacolepis incrustons Schmitz (1893), on Phyllophora nervosa

(DC.) Grev.

15. Sterrocolax decipiens Schmitz (1893), on Ahnfeldtia plicata (Huds.) Fr.

16. Sterrocolax crassior Schmitz (1893) on "Gymnogongrus fas- tigiatus var. crassior Ruprecht."

17. Ceratocolax H art z?i Rosenvinge (1898), on Phyllophora inter-

rupta (Grev.) J. Ag. 18. Callocolax ne glee tus Schmitz (1894), on Callo phyllis laciniata

(Huds.) Kuetz.

Sph^rococcace^e.

19. Gracilariophila oryzoides Setchell et Wilson (1910), on Grac'v- loria confervoides (L.) Grev.

164 SETCHELL?PARASITISM AMONG RED ALG^E.

Delesseriace^.

20. Gonimophyllum Buff homi Batters (1892), on Nitophyllum laceratum (Gmel.) Grev.

BONNEMAISONIACE^:.

21. Ricardia Montagnei Derbes et Solier (1856) on Laurencia ob-

tusa (Huds.) Lamour.

22. Ricardia Montagnei var. gigantea Farlow, on Laurencia sp.

Rhodomelaceae.

23. Janczewskia verruc?formis Solms (1876), on Laurencia ob- tusa (Huds.) Lamour.

24. Janczewskia tasmanica Falkenb. (1897), on Laurencia Forsten

(Mert.) Grev.

25. Janczewskia moriformis Setchell (1914), on Chondria atro-

purp?rea Harv. 26. Janczewskia lappacea Setchell (1914), on Chondria nidifica

Harv.

27. Janczewskia Gardnerii Setchell et Guernsey (1914) on Lauren- cia spectabilis R. & R.

28. Janczewskia Solmsii Setchell et Guernsey (1914), on Lauren- cio subopposita (J. Ag.) Setchell.

29. Microcolax botryocarpa (Hook, et Harv.) Schmitz (1897), on Streb do elodia neglecta Schmitz.

f30. Pleur ostichidium Falkenb er gii Heydrich (1893), on Xipho- phora chondrophyllo (R. Br.) Harv.

31. Colaconema pulvinatum Schmitz (1897), on Vidolia serrata

(Suhr.) J. Ag.

32. Colacodasya inconspicua Schmitz (1897), on Polysiphonia and

Heterosiphonio.

33. Colacodasya verruc?formis Setchell et McFadden (1911) on Chondria.

f34. Haplodasya Reinboldii Falkenberg (1897), on Cystophora re- tro flexa (Labili.) J. Ag.

35. Stromatocarpus parasiticus Falkenberg (1897), on Polysi- phonia virgata (Ag.) Spr.

SETCHELL?PARASITISM AMONG RED ALG^E. 165

36. Tylocolax microcarpus Schmitz (1897), on Lenormandia spec- tobilis Sond.

37. Benzaitenia yenoshimensis Yendo (1913), on Chondria crassi-

caulis Harv. and Laurencia paniculata J. Ag.

Ceramiace^.

*38. Syringocolax macroblepharis Reinsch. (1874, 75) on Gelidium

cartilagineum (L.) Gaill.

39. Episporium centroceratis Moebius (1885), on Centroceras clavulatum Mont.

Squamariace^e.

*40. Peyssonneliopsis epiphytica Setchell et Lawson (1905) on " Meredithia calif or nie a J. Ag."

CORALLINACE^E.

41. Choreonema Thureti (Bornet) Schmitz (1889), on Jania rubens Lamour and Corallina squamata E. & S.

42. Ch?tolithon d?formons (Solms) Foslie (1898), on Jania natal- ensis Harv.

In addition to the species listed above and which have been selected from the species published as being certain or very nearly so, there have resulted from collections, chiefly by N. L. Gardner, on the Pacific coast of North America, some nine additional but as

yet unpublished species, together with four additional genera, also as yet unpublished, as noted previously. All of these species are

parasitic on genera closely related to themselves. To make this more evident and, at the same time, to make known the distribution

among the families of red algae of the new genera and species, a brief resum? of these as yet unpublished species is appended. In

Sphaerococcaceae, a new species of Gracuariophilo has been found on Gracilaria Cunninghamii J. Ag. ; in Rhodymeniaceae, three new

genera of a single species each on Fauchea laciniata J. Ag., Rhody- menia Palmetto (Esp.) Grev.?, and on Plocamium coccineum

(Huds.) Lyngb., respectively; in Delesseriaceae, two new species of

Gonimophyllum, one on Nitophyllum Ruprechtianum J. Ag. and an- PROC. AMER. PHIL. SOC, VOL. LVII, L, JUNE 21, I918.

166 SETCHELL?PARASITISM AMONG RED ALG^E.

other on a species of Delesseria, as well as a single species of a new

genus on Neuroglossum Andersonianum J. Ag. ; and in Rhodo-

melaceae, two new species of S tr ornato carpus on Pterosiphonia

Baileyi (Harv.) Falkenb. and on another species of the same genus

respectively. These new genera and species are in a fairly advanced

stage of preparation towards description and illustration. In summarizing the distribution of these distinctive parasitic

genera, among the red algae, we find the results as follows :

Helminthocladiaceae .? genus with ? species. Gelidiaceae .2 genera with 5 species. Gigartinaceae .5 genera with 12 species. Sphaerococcaceae .1 genus with 2 species. Rhodymeniaceae .3 genera with 3 species. Delesseriaceae.2 genera with 4 species. Bonnemaisoniaceae.1 genus with 2 ? species. Rhodomelaceae .9 genera with 17 species. Ceramiaceae .2 genera with 2 species. Squamariaceae ..1 genus with 1 species. Corallinaceae.2 genera with 2 species.

This summary shows clearly the extent of the distribution of

parasitic genera and species through the group of the red algae and the fact that they are, thus far, known only from eleven of the

twenty-one families into which the group is usually divided. It also shows that of these eleven families, two, viz., Gigartinaceae (with 5 genera and 12 species) and Rhodomelaceae (with 9 genera and 17 species) contain one half or over of the known genera and species.

Besides the literature dealing with the strictly systematic side and describing, for the most part new species, there are a few papers which attend mostly to other matters connected with the parasitic red algae. Such, for instance, is the paper by Nott (1897) discuss-

ing the finding of certain parasitic red algae on the coast of Califor-

nia, and a similar paper by the writer published later (cf. Setchell,

1905). Sturch (1899) published the results of a careful study into the structure, development, and nature of the parasitism of Har-

veyella mirabilis Schmitz and Reinke and its systematic position. In

I9?5> Oltmanns (p. 319 et seq.) discussed parasites among the algae,

SETCHELL?PARASITISM AMONG RED ALGM. 167

particularly describing and illustrating the parasitism of Ricardia, Actinococcus, Harveyella, Janczewskia, Str ornato carpus, Choreo- nema ("Melobesia Thureti Born.") and Ch?tolithon (?{Melobesia d?formons Solms "). The penetration, reduction of the thallus and

natural relationship to the host plant are all dealt with. This is the only general discussion of the parasitism of the red algae thus far published. In 1910 Eddelb?ttel published a general account of

parasitism among the red algae, with special reference, however, to Choreocolax and Harveyella. This account dealt particularly with the systematic position of Choreocolax and Harveyella, advocating removing them from the Gelidiaceae, where they had been placed by Schmitz, and placing them among the Gigartinales, as Sturch

(1899, p. 98) had advocated. He also discussed Gracilariophila Setchell and Wilson (1910), suggesting placing it near, if not uniting it with, Choreocolax. I am unable to agree with this latter view because of 'the very different structure of the cystocarp in the two

genera, the essentials of which, viz., the different shape and ar-

rangement of the spores, Eddelb?ttel did not mention or seem to consider in his discussion.

From all the previous consideration, two things, at least, seem plain. First, there are approximately twenty-nine genera and fifty- one species of undoubted and peculiar parasites among the red algae. Doubtless there are many of similar character to be discov- ered. In fact, there is knowledge, but of unsatisfactory character, of the existence of a number of such. Doubtless also, there are some, possibly many, at least partial parasites among the various "

epiphytes " and "

endophytes," so numerous in the group. Second, there is an overwhelming restriction in the matter of

parasitism on other red algae and even on other members of the same family. Of 51 parasites enumerated above, 41 are fairly cer- tainly parasitic on another member of the same family. This is a little over 80 per cent, of the whole number. Of the remainder, 8 or a little less than 16 per cent, are parasitic on red algae not of the same family (i. e., practically 96 per cent., therefore, parasitic on other red algae), while only two or a little less than 4 per cent, are parasitic on algae (brown) other than red.

Although acquainted with a far less number of cases Batters

168 SETCHELL?PARASITISM AMONG RED ALCE.

(1892, p. 66 and 1895, p. 317), Schmitz (1893, p. 390) and Olt-

manns (1905, p. 334) have all spoken emphatically of the fact that

so many of the parasitic red algae are restricted to near relatives as

hosts. Oltmanns further remarks (loc. cit.) that no satisfactory ex-

planation of this can be brought forward. The suspicion has been

produced, especially earlier in the progress of our knowledge, that

some of these parasites, especially some species of Actinococcus, are

really parasitic tetrasporangial generations of the hosts they inhabit.

Darbishire (1899, p. 264) has voiced this suspicion and has stated

his opinion that while this is not impossible, it is not very probable. The probability, as it seems to the writer, is, however, that the various

parasites, or some of them, may have originated in close connection

with their hosts by some mutation decreasing the chlorophyll con- tent or power in one or other of the different forms of spore. Such an inducement to increase the power of penetration and possible protoplasmic connection between a spore (tetraspore or carpospore) germinating in position might, it would seem probable, initiate para- sitism on the parent plant, and this parasitic tendency increasing penetration and dwarfing, might, therefore, be inheritable.

There is one case known which seems to be such a case or in line with such action. This is the condition found in Agardhiella tenera (J. Ag.) Schmitz ("Rhabdonio tenera" J. Ag.) by Oster- hout (1896). It was noticed that the tetrasporangial plants have, in many cases, numerous short bristle-like branches or proliferations projecting at right angles to the main stem and branches, but that the antheridial and cystocarpic plants are always destitute of them. Examination showed that these peculiar branchlets are usually an-

theridial, while full-sized antheridial plants are rare. Sometimes, however, the bristly short branchlets have tetrasporangia or cysto- carps and the three kinds of reproductive bodies are sometimes borne on branchlets side by side. Some of the branchlets remain sterile "but in the majority of cases they bear reproductive organs before they are more than a quarter of an inch in length." (Oster- hout, loc. cit., p. 420.)

It was found by Osterhout that the zonate tetrasporangia divide in regular fashion forming what seem to be four tetraspores each, arranged serially. These spores then sometimes divide further by

SETCHELL?PARASITISM AMONG RED ALG^E. 169

oblique divisions and as this continues the contents of a tetrasporan-

gium act as a whole, producing penetrating rhizoidal filaments below

and a regular, though much dwarfed, Agardhiella-irond above. The

rhizoidal filaments penetrate even into the region of the medullary

hyphae of the parent plant and establish " secondary connections "

with them. There seems certainly to be here a parasitic red alga in the making. There exist full-sized plants of Agardhiella tenera of all three sorts, viz., antheridial, cystocarpic and tetrasporangial. There exist also dwarf plants, parasitic on, but arising from, the

tetrasporangial plant. While these dwarf plants, and they are very much reduced and simple, are largely antheridial, yet, according to

Osterhout,, all three kinds of dwarf plants, viz., antheridial, cystocar- pic and tetrasporangial, may exist side by side, all parasitic on and

probably arising from the same full-sized tetrasporangial plant. In order that our knowledge of this interesting and seemingly very sig- nificant case may be more complete, it is very desirable that culture be made from the spores (both carpospores and tetraspores, if ob-

tainable) of the dwarf plants. It is very desirable that this be undertaken by some investigator who has access to abundant growths of these plants. The very similar species, Agardhiella Coulteri

(Harv.) Setchell, of the California coast has not been observed to

produce dwarf plants (or bristly proliferations) from, the tetra-

sporangial generation. In summarizing, then, the aim. of this paper, it may be said to

be intended to indicate how general is the extent of the parasitism of the parasitic genera and species of red algae upon their near rela- tives and to draw attention to the similarity of these cases and the case of the production of a dwarf parasitic generation from the

tetrasporangia of Agardhiella tenera and with the hope of suggesting the probability of their origin.

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