140 FUNGOUS DISEASES OF PLANTS 



are certain members of the genus Urophlyctis. 1 ' 2 Urophlyctis 

 leproides (Trabut) Magn. occurs on root outgrowths of the beet, 

 Beta vulgaris ; Urophlyctis pulposa (Wall.) Schroet. attacks 

 leaves and stems of species of Chenopodium and Atriplex ; 

 and Urophlyctis Alfalfa (v. Lagerh.) Magn. is found upon the 

 roots of alfalfa, Medicago sativa, in South America and in 

 Germany. 



VI. SAPROLEGNIALES 



The Saprolegniales are commonly called water molds on 

 account of the fact that the majority of these fungi occur in 

 the water, usually in ponds and streams, upon dead insects and 

 other small animals, or sometimes upon other organic matter. 

 One or more species attack fish, producing important diseases. 

 A few members of the order, however, are not properly water 

 molds, being found upon plants in moist places, some parasitic 

 and some saprophytic. In the aquatic forms there is a con- 

 siderably branched mycelium, habitually without septa, except 

 where spore-producing parts are cut off. The hyphae are fre- 

 quently of large diameter and readily evident to the unaided 

 eye. Nonsexual spores are produced in terminal sporangia. 

 Upon liberation the spores usually become motile. Sexual repro- 

 duction is by means of unequal gametes, produced in oogonia 

 and antheridia. The latter are sometimes wanting; moreover, 

 when present there are cases (certain aquatic forms) where they 

 are apparently functionless. 



Pythiaceae. The Pythiaceae include such members of the 

 Saprolegniales as are important in plant pathological study. 

 The family has some characters which seem to indicate that 

 they might with equal propriety be placed in the order next 

 discussed, Peronosporales. The species which are of interest 

 in this connection are those which cause damping-off, rot, or 

 somewhat similar diseases in seedlings, or in delicate plants. 

 This family differs from the remaining coordinate members of 

 the order in the complete differentiation of the sporangia from 



1 Magnus, P. Ueber eine neue unterirdisch lebende Art der Gattung Uro- 

 phlyctis. Ber. d. deut. hot. Ges. 19 : 145-150. //. 27. 1901. 



2 Magnus, P. Ueber die in den knolligen Wurzelauswiichsen der Luzerne 

 lebende Urophlyctis. Ber. d. deut. bot. Ges. 20 : 291-296. pi. 15. 1902. 



