THALLOPHYTES 



57 



sporangia or spores or sex-organs are cut off from the rest of 

 the body ; and therefore the vegetative body is one continu- 

 ous cavity. It is the one group of Fungi that can be recog- 

 nized from its mycelium. The sexual apparatus very much 

 resembles that of the Algae, and the whole structure of the 

 body is so suggestive of Alga3 that if these were the only 

 Fungi probably no one would doubt that Fungi had been 

 derived from Algae. On 

 account of this resem- 

 blance, the group is called 

 the " Alga-fungi " (Phy- 

 comycetes). Among the 

 illustrations used above, 

 the molds and downy 

 mildews are members of 

 this group. 



In the second group the 

 mycelium has cross walls, 

 but the sex-apparatus, so 

 far as any has been found, 

 is not very suggestive of 

 the Alg33. The distin- 

 guishing mark of the 

 group, however, is the pro- 

 duction of spores within 

 a sac that has a peculiar 



origin. Therefore the group is called the " Sac-fungi " 

 (Ascomycetes) , and the lilac mildew, mentioned above, is 

 a member of it. In that plant the spore-containing sac 

 (ascus) is inclosed, usually along with others, by a case 

 (Fig. 34), but in many Sac-fungi the case does not inclose 

 the sacs, but forms disks, cups, funnels, or flasks, which the 

 sacs line. Any fungus in whose life-history these sacs appear 

 is a " Sac-fungus." 



In the third group the mycelium has cross walls, as in the 



FIG. 43. Puffballs. After GIBSON. 



