228 STRUCTURAL BOTANY 



relations. In histological structure the two genera are 

 almost identical, if we leave out of account the chloro- 

 phyll-bodies, which Pythium has given up in adopting a 

 parasitic or saprophytic mode of life. In the reproductive 

 processes there are various deviations from the algal 

 type, the most important being the suppression of the 

 spermatozoids, and the gradual replacement (only just 

 beginning in Pytftium, but more marked among its 

 allies) of zoosporangia by directly germinating conidia. 

 As we advance towards the higher Fungi we shall find 

 the algal characters dropping more and more out of 

 sight. 



TYPE XIX. PlLOBOLUS CRYSTALLINUS 



Among the Algae we found in some of our types (as, for 

 example, in (Edogonium and Vaucheria) a well-marked 

 process of fertilisation, in which the cells taking part in 

 the formation of the oospore showed a distinct difference 

 of sex. In others, however, namely in Ulothrix and 

 Spirogyra, union was found to take place between two 

 essentially similar cells, each having an equal share in 

 the act of conjugation, and the resulting formation of a 

 zygospore. Both these modes of sexual reproduction are 

 represented also among the Fungi. Our last type, Pythium, 

 afforded an example of fertilisation ; the group to which 

 it belongs bears the name of the Oomycetes. We are now 

 about to describe a form in which the sexual act is one 

 of conjugation ; the Fungi in which this process prevails 

 are called the Zygomycetes. 



A large proportion, though by no means all, of 

 the Oomycetes are parasites on living plants or animals. 

 Among the Zygomycetes parasitism, though it occurs, is 



