44 COMPARATIVE MORPHOLOGY OF FUNGI 



chromosome number appears to be from 10 to 12. After cleavage, the 

 uninucleate portions of protoplasm become zoospores liberated by 

 degeneration of the tube. 



Polyphagias stands on the dividing line between holocarpism and 

 eucarpism. Physiologically it is still holocarpic. With the formation 

 of the sporangium the plant has spent its life. Morphologically it is 

 already eucarpic, for no longer the whole but only its central portion 

 becomes a sporangium. 



At the sudden appearance of unfavorable conditions the single indi- 

 viduals may become encysted so that the central sac is surrounded by a 

 thick membrane. At the return of favorable conditions, they germinate 

 by a sporangium as above described. 



If the store of nourishment (fresh Euglenae) is exhausted, the plants 

 change to gametangia instead of germinating with sporangia. The 

 smaller, male individual forms a long thin process. On meeting a female 

 cell, this process swells to a sac which thickens its wall echinulately and 

 absorbs the whole content of the male plant. The wall between the 

 female cell and this sac is dissolved and the content of the female cell 

 is discharged into the sac (Fig. 26, 4 and 5). The smaller male and the 

 somewhat larger female nuclei do not fuse but remain diametrically 

 opposite at the periphery. The male nucleus gradually attains the size 

 of the female. Meanwhile the zygote has been separated from the 

 gametangia by two walls, it rounds off and becomes a hypnospore (Fig. 

 27, 1), while the remains of both plants degenerate. The whole process 

 lasts at most 12 hours. 



After a few months the zygote germinates by a zoosporangium into 

 which both sexual nuclei pass and fuse (Fig. 27, 2 and 3), whereupon, 

 possibly, meiosis follows at once. The life cycle may be represented by 

 the following scheme: 



I 

 ± Thallus— +Zoosporangiurn — ^Zoospores 



/ P C R 



Zoospores ^+ Tli all us >- + Coenoganiete Hypnospores— ^oosporangium 



^ — Thallus >-— Coenogamcte 



Diagram V. 



Thus from one zoospore there arises a unicellular thallus which can 

 form a zoosporangium or a gametangium, with copulation between 

 unicellular coenogametes. In this scheme it is uncertain whether the 

 zoospores throughout the whole period of vegetation may be considered 

 as + and — in the sense of heterothallism, or whether they and their 

 thalli, as assumed in this scheme, are indifferent throughout, with sexual 

 differentiation only in the formation of individuals behaving as gametan- 

 gia. In contrast to Olpidium Viciae (p. 18) the diplont is here reduced 

 to the hypnospore. 



