SETCHELL— PARASITISM AMONG RED ALG^. 167 



particularly describing and illustrating the parasitism of Ricardia, 

 Actinococcus, Harveyclla, Jancsewskia, Stromatocarpus, Choreo- 

 nema {" Mclohesia Thiireti Born.") and Chcctolithon (" Melobesia 

 deformans 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 algse thus 

 far published. In 1910 Eddelbiittel published a general account of 

 parasitism among the red algse, with special reference, however, to 

 CJwreocolax and Harvcyella. This account dealt particularly with 

 the systematic position of CJwreocolax and Harveyclla, advocating 

 removing them from the Gelidiace^e, 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, Eddelbiittel 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 

 algse. 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 algse 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. c, practically 96 per cent., therefore, parasitic on 

 other red algse), while only two or a little less than 4 per cent, are 

 parasitic on algse (brown) other than red. 



Although acquainted with a far less number of cases Batters 



