THE FUNGI 



161 



B 



gametes. The cell-wall separating the two cells now is absorbed and their con- 

 tents fuse. Whether the nuclei fuse in pairs, as in Albugo bliti, is not known, 

 but it is not improb- 

 able. The zygote A 

 increases greatly in 

 size, at the expense 

 of the protoplasm in 

 the branches upon 

 which the gametes 

 were formed. It be- 

 comes finally filled 

 with dense granular 

 contents, and the 

 wall becomes black 

 and opaque. The 

 ripe zygote (zygo- 

 spore) shows three 

 membranes, the out- 

 er of which is formed 

 from the original 

 membrane of the 

 conjugating cells. 



FIG. 125. A, Piptocephalis Freseniana (X 300). (After 

 BREFELD.) B, G, Pilobolus crystallinus (B, X25; C, 

 X 50) ; w, drops of water; sp. sporangium. 



In Piptocepha- 

 lis the zygospore 

 is formed as an outgrowth at the point of junction of the gametes, 

 and not by their direct fusion. In Mortierella the zygospore is sur- 

 rounded by a dense growth of hyphae, which completely conceals it. 



Order II. Entomophthorineae (Thaxter, 20) 



The Entomophthorineae are Fungi parasitieupon insects of various 

 kinds, which are killed by their attacks (Fig. 126). The commonest 

 form is Etnpusa muscce, which attacks the common house-fly. The 

 infested flies are sometimes met with, especially in the autumn, stuck 

 to window-panes, and surrounded by a whitish halo of the Fungus- 

 spores. The germinating spores penetrate the body of the insect, 

 probably through the thin membrane between the rings of the body 

 or through the stigmata. Within the body of the host, the Fungus 

 grows rapidly, forming, by budding, a great number of short hyphal 

 joints, which sometimes become dormant for a longer or shorter period. 

 After these have completely exhausted the nutritive matter from the 

 host, which then dies, if suitable conditions of temperature and mois- 

 ture are provided each hyphal body develops one or more basidia 

 which break through the thin places in the integument of the insect. 

 Upon emerging, each basidium has cut off from its extremity a 

 single conidium, or perhaps more exactly a sporangium containing a 

 single spore which completely fills it. These conidia are shot off, 



