CHAP. 11.] CHEMISTRY, ETC., OF PLANT LIFE. 83 



scope, a number of spores as already described will be 

 seen, but mixed with these, and produced by the same 

 niycelium or vegetative portion of the fungus, will be 

 found spores of a totally different form and colour, each 

 consisting of two superposed cells furnished with a smooth, 

 brown cell- wall; as the season advances, the streaks 

 formed on the stem and leaves are almost black, and on 

 examination the spores will be found to consist entirely of 

 the last described two-celled kind, the one-celled first 

 formed kind having entirely disappeared. If the above 

 explanation has been understood, it will be seen that the 

 fungus during its development has completely changed 

 the nature of its spores or reproductive bodies not only 

 in colour and structure, but what is of more importance, 

 in function also ; the two-celled spores produced in the 

 autumn cannot germinate at once when mature, but pass 

 the winter in an unaltered condition, being carried to 

 the ground by the fall and decay of the leaves or stems 

 on which they are produced. The following spring these 

 spores germinate as follows : each cell of the spore 

 produces a short slender branch or germ- tube, that pro- 

 duces near its tip two or three very minute spores called 

 promyeelium spores. These minute spores can only ger- 

 minate when carried by wind or some other means on to 

 the surface of the newly-expanded leaves of the common 

 barberry (JBerheris vulgaris) ; when once located in this 

 position germination commences, and soon a slender 

 germ-tube is produced by the spore, that at once bores 

 through the epidermis of the leaf, and develops a 

 mycelium or vegetative portion at the expense of the 

 leaf; after a time the mycelium produces dense clusters 

 of yellow spores, at first arranged in chains, inclosed in 



