74 



THE FUNGI WHICH CAUSE PLANT DISEASE 



ficial and does not extend to the fleshy tap root. The develop- 

 ment of the spores is the typical method for the genus, the an- 

 theridium persisting at the base of the oogonium and retaining its 

 hyphal connection, while the oogonium becomes free just before 



conjugation. The oospores are 

 subglobose, depressed on one side, 

 smooth, brown, 45-50 x 30 fi. 



U. pulposa (Wallr.) Schr., a 

 closely related species occurs on 

 the aerial portions of Chenopo- 

 dium and Atriplex. 



U. alfalfse Mag.'"' *'^' ^^' "^' "^ 

 causes a crown gall of alfalfa in 

 America and Europe. The dis- 

 ease is quite similar to that de- 

 scribed above for the beet. 



U. trifolii (Pass.), Mag., a 

 closely related ^ecies, forms 

 small, glassy, globose pustules on the leaves and petioles of 

 various species of clover in Europe. 



U. hemispherica (Speg.) Syd.*^ in South America, U. krieger- 

 iana Mag." in Europe and U. pluriannulata (B. & C.) Farl.'^ 

 in America form Synchytrium-like galls on various umbeUiferous 

 genera. All may belong to the same species. U. major Schr. and 

 U. rubsaameri Mag. infect respectively the leaves and the roots of 

 Rumex. 



Fig. 44. — Urophlyctis pulposa. a, zoo- 

 aporangium; 6, zoospores; c, oospore 

 formation ; d, mature oospores. After 

 Schroter. 



Saprolegniales (p. 66) 



Asexual reproduction is mainly by biciliated spores formed in 

 large numbers in sporangia of various shapes. Sexual spores, 

 often apogamous, are produced in most genera, much after the 

 fashion of those of the Peronosporales except that more than one 

 oospore is frequently formed in one oogonium.^** 



The order consists of fifty or more species, mostly parasites 

 or saprophytes upon aquatic organisms. One species of the genus 

 Achlya causes serious disease in young fish. 



There are three families: 



