PMYCOMYCETES.— (a) OOMYCETES 



z|2i 



moving freely in water, offers an interesting parallel with the pollen- 

 tube in Seed-Plants. In both cases the male gamete is conveyed 

 to the female by a method suitable for land-living plants. Comparison 

 shows that both are modifications of organs originally developed 

 to secure fertilisation through the medium of external water. The 

 question will naturally arise whether any fungal type still shows a 

 motile male gamete. This is found in Moiwblepharis, a fungus that 

 lives saprophytically in water (Fig. 35S). Here a terminal oogonium 



Fig. 356. 

 Germination of zoospores of PhytopJUhora on the epidermis of Potato. At {a) 

 the germ-tube is entering a stoma. At (c) it bores directly through the ceU-wall. 

 Highly magnified. (After M.arshall Ward.) 



contains a single ovum, which is fertilised by spermatozoids, each 

 motile by a single cilium. This case is unique among Fungi. It 

 holds a place comparable with the motile spermatozoids of the Cycads 

 and Ginkgo, as evidence of the transition from an aquatic to a 

 terrestrial type of fertilisation. (Compare Chapter XXXII.) 



The origin of such Phycomycetous Fungi as those described was 

 probably from some Siphonaceous source. In the case of para- 

 sites the first step would be the adoption of an endophytic life, 

 as in Phyllosiphon. This would be naturally follow-ed by parasitic 

 nutrition and loss of chlorophyll and chloroplasts. As regards 

 the propagative organs, the conidium of Pythium or of Phytophthora 

 represents a zoo-sporangium modified for separation and transport 



