234 STRUCTUKAL BOTANY 



wall, and forms a quantity of oil in its contents. We 

 see that the process is one of perfectly typical conjuga- 

 tion, the two cells concerned taking an exactly equal 

 part in the production of the zygospore. 



After a period of rest, the zygospore, if moistened, 

 germinates. The germination is best known in an allied 

 genus, Mucor. If food enough is to be had, it simply 

 grows out at once into a new mycelium; if, however, 

 supplies are scanty, it proceeds without delay to form 

 an asexual sporangium, thus increasing the chances of 

 survival. These differences are quite analogous to those 

 which we found in the germination of the oospores of 

 Pythium. 



The Zygomycetes, so far as their sexual reproduction 

 is concerned, stand on a lower level than the last group. 

 On the other hand, they are more fully adapted to a 

 terrestrial mode of life, and so far are more perfect, as 

 Fungi, than the Oomycetes. We saw in the case of 

 Peronospora how a transition can be traced from the 

 sporangium to a single conidium, germinating directly. 

 A somewhat similar gradation is to be followed among 

 the immediate relations of Pttdbohis. Some of these 

 produce, in addition to the typical large sporangia, very 

 small sporangioles, containing very few spores, or even 

 only one. In other species sporangioles only are known, 

 and these become detached bodily from the supporting 

 hypha, and behave like single conidia. Thus in the 

 Zygomycetes, as in the Oomycetes, a succession of steps 

 leads from the typical sporangium to the simple conidium, 

 the most characteristic form of reproductive cell in the 

 Fungi 



