396 



EXPERIMENTS WITH PLANTS 



The spores of the Mould are (like the spores of the 

 bacteria) resistant cells which are not injured by 

 exposure to dry air and are, in fact, carried about by 

 the wind so as to scatter the Mould everywhere. When 

 ripe the spore-case bursts, so as to set the spores 

 free. 



In addition to these spores (called asexual spores) 

 there often occur larger ones (called sexual spores, 



or zygospores, because 

 they result from the union 

 of two branches), which 

 are formed, as shown in 

 Fig. 220, by two branches 

 coming together and fu- 

 sing so as to form a large, 

 thick- walled spore of a 

 deep black color. These 



220. Formation of zygospores of the black SpOrCS arC larger, mOre 

 Mould of bread: at the left two branches . . 



touching, to the right stages in the fu- rCSlStaut, COUtam mOl'C 

 sion, the last being the fully formed zygo- 



sp^^^- nutriment and give rise 



on germination to a more vigorous growth than the 

 ordinary asexual spores. 



Another very common Mould is the Green Mould 

 (Penicillium) of cheese, bread, jellies, etc. In this 

 Mould the spores are in long chains at the end of the 

 stalk (Pig. 221), and are not enclosed in a spore-case, 

 as in the Black Mould. 



What effect do these Moulds have on the substances 



