ASCOMYCETES 



421 



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 penultimate cell forms 

 the single ascus, with eight ascospores (Fig. 319, C. s.). Protected by 



a_ A 



Fig. 319. 

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

 the contact of the two short branches (^4), 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. (C. D.) Highly magnified. 

 (After De Bary.) (From Marshall Ward.) 



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. 



This is one of the simplest of Ascomycetous fruits. In Erysiphe 

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

 bear numerous asci. The fruit-bodies of the larger Ascomycetes are 

 in general more complex. 



Moulds (Plectascales). 



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 germs 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 



