92 EVOLUTION OF PLANTS 



The spore-fruit in these mildews is very simple, and 

 in most cases is preceded by the formation of an archi- 

 carp and antheridium (Fig. 24, B), both of which are 

 simple cells cut off from special branches. These 

 organs unite, and the contents, including the nuclei, 

 fuse, and thus a true fertilization is effected, much as 

 in the white rust described under the Phycomycetes. 

 In the simplest of the mildews the fertilized archicarp 

 divides into a few cells, one of which grows directly into 

 an oval sac in which, after a preliminary division of the 

 nucleus into eight, there is formed about each of these 

 nuclei an aggregation of protoplasm which becomes sur- 

 rounded by a cell-wall and forms a spore. There are 

 still simpler Ascomycetes where the fertilized archicarp 

 becomes at once transformed into the ascus. From the 

 filaments close to the archicarp there grow out a num- 

 ber of short branches which form a compact covering 

 about the asci, the whole structure forming the " peri- 

 thecium " or spore-fruit of the mildew. In many of the 

 mildews the cells forming the wall of the perithecium 

 develop hair-like appendages of curious and characteris- 

 tic shapes, which constitute one of the best means of dis- 

 tinguishing the different genera and species. 



Closely related to the mildews is the common blue- 

 mould, Penicillium, and the herbarium-mould, Euro- 

 tium. These are saprophytes, and the spores are borne 

 on branching conidiophcres instead of in simple chains. 



The spore-fruit of some of the larger Ascomycetes 

 is very conspicuous, and in the case of the pretty cup- 

 fungi of various vivid colors, scarlet, orange, yellow, etc. 

 These large spore-fruits are usually the product of a 

 number of archicarps, i.e. they are compound in nature. 



