CHYTRIDIALES 115 



lack by chytrids can frequently be followed with comparative ease. 

 Careful observations on the early stages in the infection of the host 

 have been recorded by several investigators, notably Scherffel and 

 Couch. Scherffel (1925b) records that the first visible reaction of Tri- 

 bonema cells attacked by Chytridium confer me was the concentration 

 of plasma at the point of entrance of the infection tube. The host 

 nucleus was displaced from its central position in the cell and moved 

 to the point of infection. Secretion of wall material then occurred in 

 an attempt to stop the further incursion of the parasite. It was this 

 displacement which suggested to Scherffel the possibility that the nu- 

 cleus may have a definite role in the formation of the wall material. 

 Couch (1932) has described the reactions of the protoplast of Spirogyra 

 to the growing rhizoids of the epibiotic Rhizophydium couchii. Where 

 several young thalli were being formed at one point on the host a 

 violent rotation of the cytoplasm of the alga was apparent, and sug- 

 gested an attempt to ward off the invading rhizoids. As a result of this 

 activity on the part of the host abnormal development of the rhizoids 

 sometimes ensued. Certain of these rotating cytoplasmic streams com- 

 municated directly with the pyrenoids, a fact considered of some sig- 

 nificance since it is the stored food material of these pyrenoids which 

 is utilized by the developing fungus. As the course of the infection pro- 

 ceeded, the pyrenoids were destroyed, their starch was hydrolized, 

 and the cytoplasmic membrane along with the chloroplasts became con- 

 tracted and concentrated around the region of the rhizoids. Ultimately 

 disintegration of the whole contents took place. 



At times the host is stimulated to abnormal growth, a fact first 

 noted by Braun (1856a: 72) in regard to the swelling of Stigeoclonium 

 cells infected by Rhizophydium mammillatum. Cells of Zygogonium in- 

 fected by Micromyces zygogonii (Dangeard, 1889b) show a pronounced 

 swelling of the wall. As the fungus develops the deformed chloroplasts 

 shrink, while the hypertrophy of the wall becomes more pronounced. 

 Eventually the whole contents are consumed, and the reproductive 

 body of the chytrid lies in the distended cell. Infected cells of other con- 

 jugates attacked by species of Micromyces may at times be bent, 

 swollen, or even burst. Canter (1949c) has indicated that species of 

 Micromyces do not always cause hypertrophy of their algal hosts. 



