106 PLANT-LIFE 



tion can readily be obtained by soaking a piece of bread 

 and keeping it under an inverted tumbler. Moulds of 

 different kinds will appear rapidly; among them, on 

 about the fifth day, Mucor mucedo will be prominent. 

 It is at first white and woolly; unb ranched stalks rise 

 from it, and these stalks terminate in round knobs, 

 white at first, but later turning black. The branched 

 hyphae of the mycelium are non-cellular, like those of 

 Pythium ; they penetrate and ramify through the sub- 

 stance of the bread, obtaining nourishment therefrom. 

 The unbranched stalks which rise into the air are spor- 

 angiophores — i.e., bearers of sporangia — and the knobs 

 that terminate the stalks are the sporangia, or spore- 

 cases. The contents of the sporangia are divided into 

 numerous oval, smooth-walled spores, which are not 

 ciliated and are evidently adapted to land conditions. 

 These spores germinate under favourable conditions and 

 give rise to new mycelia. The sexually formed zygo- 

 spores, already referred to, become invested in a thick 

 membrane and can remain dormant for a protracted 

 period without loss of vitality. Mucor is certainly 

 better adapted for a terrestrial existence than Pythium, 

 and it is more completely fungal in its habits. The 

 Zygomycetes, as a whole, are more terrestrial and far 

 less parasitic than the Oomycetes, and it may be added 

 that the sexual act occurs only when the conditions 

 are not favourable to the formation of sporangia. The 

 more completely fungal the plant, the less does sex 

 appear; in the most advanced Fungi it is not in evidence. 

 About 120 species of Zygomycetes have been distin- 

 guished. 



Dire plant diseases are caused by the Rust and 



