158 



BOTANY 



Among the common Peronosporineae may be mentioned Phytoph- 

 thora infestans, the Potato-fungus ; Plasmopara viticola, the Vine- 

 mildew ; Peronospora Schleideni, the Onion-mould, as well as many 

 other destructive species. 



FIG. 122. A, C, Albugo Candida. A, young sexual organs (X 450). B, oogonium, 

 with antheridial tube penetrating the egg, which contains a single nucleus. C, the 

 fertilized egg surrounded by a membrane, outside of which lies the zone of nucle- 

 ated periplasm (x 525). D, A. bliti, oogonium with ripe spore (X 525). (B, C, 

 after WAQER.) 



SUBCLASS II. ZYGOMYCETES 



The Zygomycetes, of which the Black-moulds are the most famil- 

 iar examples, differ from the other Phycomycetes in not producing 

 motile reproductive cells. Where a sexual reproduction is known, it 

 consists in the fusion of two similar cells by a process of conjuga- 

 tion not unlike that of the Conjugates, but it is not likely that this 

 resemblance indicates any relationship between the two groups. 

 There are two orders, Mucorineae and Entomophthorineae, the for- 

 mer being mostly saprophytes, the latter parasites. 



Order I. Mucorineae 



The order Mucorineae includes several families, mostly saprophytes 

 but some parasitic, known popularly as Black-moulds, as the spores 

 and fruiting hyphae are usually black. As a type of the order 



