156 SETCHELL— PARASITISM AMONG RED ALG.^. 



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 Ascopliyllum nodosum (L.) Le Jolis has been no- 

 ticed. R. J. Harvey Gibson (1891, p. 132) states that "The attach- 

 ment of the epiphyte to Ascopkyllnm 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 hyphse." A similar penetration of the 

 " host " usually takes place from the base of Ptcrosiphonia Woodii 

 (Harv.) Falkenb. into the tissues of the Laminariacese 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 calif ornica Farlow 

 and also of an unnamed species of Callithamnion into the fronds of 

 '■'■ Callymenia Phytlophora 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 PfcrosipJionia 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 

 Bindcri J. Ag. and Ceramiiim 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 Codiitiii. This does not seem to indicate true 

 parasitism. 



Among the marine species of Chantrausia (or Acroclucfiiiiii) 

 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 



