SETCHELL— PARASITISM AMONG RED ALG^. 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 Porpliyra umbUicalis. 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 Acrochcrtiim alluded to above, there 

 are Schmitsiella cndophlaa Bornet & Batters and Rhodochorton 

 memhranaceiim Magnus. These are simply within the outer mem- 

 branes, the former of Cladophora, the latter of Sertidaria, one of 

 the Bryozoa. Somewhat more deeply, and also partially, endo- 

 phytic is Rhodochorton snbinimersum 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 algse 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 algse 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 



