432 



BOTANY OF THE LIVING PLANT 



hyphae cross or touch one another. Two short branches grow erect, 

 and a uni -nucleate cell is shut off from the end of each. One which is 

 larger is recognised as the oogonium, the other which is smaller is the 

 antheridium. They fuse, and the nucleus of the latter passes into the 

 former, which, then becomes surrounded by an investment of up- 

 growing filaments, forming an outer shell to the fruit. Meanwhile 

 the oogonium divides into a row of cells, and the terminal cell forms 

 the single ascus, with eight ascospores (Fig. 365). Protected by the 

 outer shell, and attached by long filaments which grow out from 

 their surface, the fruits remain fixed to the leaves, which fall and 

 rot. In the following spring they rupture, and the ascospores are 

 shed. In favourable conditions germination ensues. 



D 



FIG. 365. 



. Various stages in the development of the perithecium of the Hop-mildew, showing 

 the contact of the two short branches (A ), one of which (p) gradually becomes invested 

 by enveloping branches (B) . The envelope forms the wall of the perithecium, and the 

 single ascus is formed from the enclosed branch. Highly magnified. (After De 

 Bary.) (From Marshall Ward. ) 



This is probably the simplest type of Ascomycetous fruit. In 

 Erysiphe and others hyphae are produced from the female organ, and 

 they bear numerous asci. Such developments lead on to the more 

 complex fruit-bodies of the larger Ascomycetous Fungi. 



Mo u LDS (Plectascineae) . 



If bread, or any organic body such as leather or jam, be kept in a 

 closed damp space, for instance under a bell-glass, or in a damp 

 cupboard, it will become mouldy. This is due to the germination 

 upon it of air-borne spores of Moulds that are always present about 

 the dwellings of man. These Moulds at first form isolated patches on 

 the bread, which then run together, covering the whole surface, and 

 also penetrating inwards. There are many different Moulds that 

 may thus appear, and they grow mixed together, or they may be 

 segregated into distinct, purer patches. Where this occurs the two 



