18 



COMPARATIVE MORPHOLOGY OF FUNGI 



In Olpidium Viciae, which in spring and early summer causes a disease 

 of Vicia unijuga in Japan (Kusano, 1912), the uniflagellate zoospore 

 swims about on the leaves of the host for as long as 24 hours, with short 

 rest periods during which it may creep over the substrate in an amoe- 

 boid manner (Fig. 9, 1). When it finally comes to rest it withdraws its 

 flagellum, surrounds itself with a membrane, bores through the wall 

 and discharges its thick naked protoplasm into an epidermal cell of 

 the host, where it attaches itself to the nucleus as an amoeboid proto- 

 plast (Fig. 9, 2 to 6). A period of promitotic (or amitotic?), later of 

 mitotic, nuclear division follows, during which the protoplast is sur- 

 rounded by a membrane and develops to a sporangium. At maturity 



Fig. 9. — Olpidium Viciae. 1. Zoospores. 2 to 5. Shedding of membranes and pene- 

 tration of host cell. 6. Naked thallus of fungus in host cell. 7. Germinating zoosporan- 

 gium. 8. Empty zoosporangium. 9. Copulation of two planogametes. 10. Young 

 zygote before caryogamy. 11. Mature hypnospore. 12. Multinucleate hypnospore at 

 the beginning of germination. (1 to 9 X 535; 10 X 600; 11, 12 X 1,200; after Kusano, 

 1912.) 



(after 5 to 10 days) this pierces the wall of the host cell by rostrate 

 processes and through one of these discharges the zoospores (Fig. 9, 

 7 and 8). 



Under certain conditions, the zoospores behave as planogametes, 

 especially in very ripe sporangia which have consumed the nutriment of 

 the host cell and, while waiting for favorable conditions of nutrition, 

 are passing through a period of hunger. Then they copulate in pairs 

 during pauses in their amoeboid activity. The biflagellate zygote swims 

 about (also with rest periods) and finally comes to rest, surrounds itself 

 with a membrane and discharges its content into a host cell. A definite 

 point of fusion is not present as in the planogametes of the Chlorophyceae; 



