ASCOMYCETES 



129 



pendent of the sexual organs, by the physiological stimulation of nourish- 

 ment, and the sexual organs are later formed in them. 



As was the case in the Endogonaceae, so also in the Ascomycetes, 

 plasmogamy is not followed directly by caryogamy but one or several 

 dicaryons are formed (according to the number of gametangial nuclei). 

 In the lower forms the dicaryon migrates directly into an ascus (as 

 into the zygote of Endogone) which is formed as the product of the 

 plasmogamy. In the higher forms, caryogamy is more and more retarded 

 and the fertilized gametangium develops into one or more hyphae which 

 take up the dicaryon and, by conjugate division, branch and proceed to 

 the formation of asci. These dicaryotic hyphae are called ascogenous 



Fig. 79. — Pyronema confluens. Development of ascogenous hyphae. 



Claussen, 1912.) 



(X 1,165; after 



hyphae; biologically they offer the advantage that, in contrast to the 

 lower forms, one gametangium can create a number of asci. 



In most of the higher Ascomycetes, the asci arise on the ascogenous 

 hyphae according to the hook type. In this connection may be men- 

 tioned Pyronema confluens. The ascogenous hyphae springing from the 

 ascogonium are coenocytic, i.e., they contain a number of dicaryons 

 (Fig. 221, 1), and develop by repeated forking, more or less vertically 

 toward the top of the future fructification. Subsequently they divide 

 by septa so that in the neighborhood of the ascogonium, the cells contain 

 2 to 8 dicaryons and farther away only one (Fig. 221, 2). A cell with 

 only one dicaryon puts forth a lateral process whereby the nuclei become 



