CHYTRIDIALES 197 



to a species which differs from the present one in not causing hyper- 

 trophy of the algal cell and in forming the sorus at the tip of a narrow 

 canal on the outside of the host. 



The presence of distinct hypertrophy in infected cells has been 

 noted by all observers of Micromyees zygogonii, as has also the at- 

 traction of the young thallus for the host nucleus rather than for the 

 chloroplast. The infected cell may become from two to three times 

 longer and wider than healthy cells. Lateral expansion is often ac- 

 companied in its later stages by a strong bulging out of the side wall. 

 This wall may fracture at its apex and allow for the passage of the un- 

 digested contents of the alga. If disintegration of the algal wall does 

 not take place elsewhere the same orifice undoubtedly also allows the 

 zoospores access to the outside medium. Heidt, who maintained in- 

 fected algae for months in 1 per cent agar, observed that the parasite 

 could cause elongation not only of the whole cell but also of a part 

 of the cell and that the same parasite might in one culture bring about 

 complete disintegration of the cell and in another only slightly affect 



Explanation of Figure 16 



A-B. Micromyees longispinosus Couch in Spirogyra: A, portion of cell of 

 Spirogyra with two young thalli (p) attached to host nucleus («); B, nearly 

 mature spiny thallus attached to host nucleus. C. Micromyees zygogonii 

 Dangeard, part of empty Mougeotia cell with discharged spiny prosorus 

 (p) and four sporangia (sp); uppermost sporangium is discharging zoospores. 

 D-E. Micromyees cristata var. cristata (Scherffel) Sparrow in Hyalotheca: 

 D, empty endobiotic resting spore (seen from top), with the tube and epi- 

 biotic rough-walled sorus (s) of sporangia to which it has given rise; spiral 

 arrangement of spines on resting spore is clearly seen; E, smooth-walled 

 endobiotic resting spore and, connected to it by a tube, the ruptured sorus, 

 within which are undischarged sporangia; several empty sporangia (sp) have 

 fallen away from the group. F-G. Endodesmidium formosum Canter in Ne- 

 trium : F, two germinated prosori with discharged sori ; the cystlike sporan- 

 gia have produced zoospores both inside and outside the host cell; G, mature 

 sorus discharging nonswarming amoeboid structures (one bearing a flagel- 

 lum) which will encyst and function as sporangia. H. Micromyees mirabilis 

 (Canter), comb, nov., in Closterium; large prosorus with immature external 

 sorus showing beginning of differentiation into sporangia. 



{A-B, Couch, 1931; D-E, Scherffel, 1926a; F-H, Canter, 1949c) 



