XVI. OBSERVATIONS ON CHLOROCHYTRIUM. 



E. M. FREEMAN. 



In 1850 Mettenius found numerous green cells in the thallus 

 of Polyides lumbricalis which resembled closely what are 

 now classified as the Endosphasreae of the Protococcaceae. He 

 interpreted them as spore-mother cells of the red seaweed 

 upon which they were found. Thuret fourteen years later 

 observed these same structures and interpreted them as parasitic 

 zoospores which on germination produce the bushy thallus of 

 Cladophora lanosa. Cohn in 1865 was able to confirm the 

 observations of Mettenius and of Thuret, except as to the germ- 

 ination of the endophyte into Cladophora lanosa. 



The condition of endophytism was considered at that time as 

 indicative of parasitism. Hence new interest was aroused in 

 the investigation of these lower forms when Rees and Schwen- 

 dener at about the same time (1871) advanced independently 

 the theory that the Cottema type of lichen is to be derived from 

 a discomycetous fungus, the mycelium of which has pene- 

 trated the mucilage of a Nostoc completely surrounding the 

 latter. Reinke's observations on Nostoc in the stems of Gun- 

 ner a scabra and the work of Milde and Janczewski on Nostocs 

 in liverworts demonstrated the occurrence of Protococcus-like 

 algal forms in the plant tissues of higher plants. Cohn in 

 1872 suggested that the presence of the Nostoc filaments in 

 Gunner a and Anthoceros is perhaps to be explained as an acci- 

 dental entry of the movable Nostoc filaments into the tissues of 

 the nurse plant, their continued growth in this new sheltered 

 position and their subsequent imprisonment by the growth of 

 the surrounding tissues of the nurse plant. In contrast to this 

 form of endophytism Cohn describes the new genus Chloro- 

 chytrium, which he considers to be a true parasite in certain 

 species of Lemna. The zoospores, very numerous on the sur- 

 face of the host, send out a germination tube between two epi- 



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