PHYCOMYCETES.— (^) OOMYCETES 



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

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

 to the female by a method suitable for land-living plants. Comparj^^on 

 shows that both are modifications of organs originally developed 

 to secure fertiHsation 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 Monoblepharis, a fungus that 

 lives saprophytically in water (Fig. 358). Here a terminal oogonium 



Fig. 356. 

 Germination of zoospores of Phytophthora on the epidermis of Potato. At (a) 

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

 Highly magnified. (After Marshall Ward.) 



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

 motile by a single cilium. This case is unique among Eungi. 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 XX.XII.) 



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 followed by parasitic 

 nutrition and loss of chlorophyll and chlorophists. As regards 

 the propagative organs, the conidium of Pythium or of PhytophUund 

 represents a zoo-sporangium modified for separation and transport 



