166 



BOTANY 



The vegetative portion of the Fungus consists of irregular, thick-walled, undi- 

 vided hyphae, which follow closely the intercellular spaces in the stem and 

 leaves. Toward the outside of the stem, where the cells are smaller, the hyphse 

 become very irregular and much branched, their extremities forming close tufts 

 of short branches just below the epidermis. The haustoria, which are freely 

 developed, are little globular bodies connected with the hypha by a slender neck 

 (Fig. 121, D). The protoplasm of the hypha is multinucleate. 



Conidia. The non-sexual spores, or Conidia, are cut off in succession from 

 the short terminal branches of the hyphae. These conidial branches are known 

 as "Basidia." The end of the basidium becomes somewhat enlarged, and 

 slightly constricted, and is finally cut off by a transverse wall. This process 

 is repeated until a chain of oval spores is produced, the lowest ones being the 



E 



B 



og- 



FIG. 120. A, B, Monoblepharis insignis ; og, ob'gonium ; 5 antheridium. C, Myrio- 

 blepharis paradoxa, development of the multiciliate zoospores, sp. D, E, Rhi- 

 phidium Americanum, zoosporangium ( X 280) ; in E, the biciliate zoospores, 

 F, are escaping. (All after THAXTER.) 



last formed. In the young conidium the basal wall is thick, and most of this 

 thickened wall becomes later absorbed, leaving only a narrow neck between the 

 conidia, which are then very easily broken apart. With the growth of the 

 conidial masses, the epidermis of the host is finally ruptured, and the spores are 

 thus set free. 



Germination. Each conidium (Fig. 121, F) is an oval cell containing several 

 nuclei. The conidia germinate promptly if supplied with water, the contents 

 of each conidium dividing into as many parts as there are nuclei, and escaping 

 from the conidium (zoosporangium) very much like the zoospores of Saproleg- 

 nia. The zoospores are bean-shaped, with two lateral cilia. After a short 

 period of activity they come to rest, and send out a germ-tube which penetrates 

 the tissues of the young seedling plant or the very young axillary buds of the 

 older ones. 



