THE FUNGI 



155 



num, is the cause of the disease of young seedlings called " damping- 

 off," the Fungus attacking the plant close to the ground, and causing 

 the stem to rot off. The 

 reproduction in Pythium 

 is much like that of the 

 true Water-moulds. 



Monoblepharis, etc. Sim- 

 ilar in many respects to 

 the Water-moulds, are a 

 number of curious aquatic 

 Fungi, which have been 

 especially studied by Pro- 

 fessor Roland Thaxter (22). 

 One of these, Myrioble- 

 pharis (Fig. 120, C), has 

 large multiciliate zoospores 

 like those of Vaiicheria. 

 Monoblepharis (Fig. 120, 

 A, B) has uniciliate zoo- 

 spores, and fertilization is 

 effected by motile sperma- 

 tozoids, as in the Chloro- 

 phycese. 



Order III. 

 Peronosporineae 



FIG. 119. A, Rhiphidium Americanum, fertiliza- 

 tion of the oogonium by antheridium ; 6 ( X 240) . 

 (After THAXTER.) B, Achlya Americana, fer- 

 tilization (X 300.) (After TROW.) C, D, Sap- 

 rolegnia ferax, development of the oogonium 

 (X 110) ; the oqspores, D, develop without fer- 

 tilization. 



This very characteristic 

 order includes a number of 

 very destructive parasitic 

 Fungi, causing some of the most serious diseases of plants. The 

 Fungus lives within the tissues of the host plant, occupying the 

 spaces between the cells into which suckers (Haustoria) are sent, 

 by which the parasite absorbs the contents of the cells. 



Albugo Candida. One of the best known of the Peronosporineae 

 is the " White-rust " (Albugo Candida), which often attacks the Shep- 

 herd's-purse (Capsella) and other Cruci ferae, where its growth causes 

 great deformation of the host, the flowers and young fruits being 

 especially affected (Fig. 121). The common name is derived from 

 the white blisters which are produced by the masses of spores formed 

 below the epidermis of the host. The epidermis is finally broken 

 through and the masses of spores set free. In the Eastern States, a 

 common species is A. bliti, which grows upon the Pigweed (Ama- 

 rantus sp.) and allied plants and A. portulacce, upon the Purslane 

 (Portulaca oleracea). 



