12 BROOKLYN BOTANIC GARDEN MEMOIRS 



gone would still represent the nearest approach of the phycomycete 

 type to the ascomycete type. The method of conjugation of the 

 gametangia, and the growth of the zygote, in Endogone sphagnophila, 

 is surprisingly like that in Eremascus fertilis and in Dipodasciis. Even 

 without the knowledge of germination of the resting zygotes in Endo- 

 gone, the genus seems to offer more of the characteristics of a prototype 

 of the Protoascomycetes (and perhaps also of the Uredinales) than 

 any other known phycomycete.^ Endogone presents additional strong 

 evidence of the phycomycete ancestry of the Ascomycetes. 



All of the evidence considered, it appears to point more strongly 

 to the zygomycete alliance as the source of the primitive ascomycete 

 stock, rather than to the oomycete alliance. In the oomycetes the 

 sexual organs and the processes of fertilization have become very 

 highly specialized. The sexual organs are highly differentiated; one 

 or more distinct eggs are differentiated in the oogone, in many cases 

 the protoplasm being differentiated into ooplasm and periplasm; 

 while a special fertilization tube from the antherid penetrates the 

 oogone, or in a rare and specialized case a motile sperm enters the 

 oogone through a pore (Monoblepharis) . 



In the zygomycetes the sexual organs have retained a simple and 

 generalized condition. Copulation is by pore formation with merging 

 of the content of the gametangia. In most cases the gametangia are 

 equal and the zygotes mature in situ, within and comprising all of 

 both gametangia. Progression in the zygomycetes, however, is mani- 

 fested in five directions. 



1. In a tendency to differentiation in size of the gametes. 



2. A tendency to differentiation of the gametangia in function, 

 the larger one becoming the receiving gametange, the oogone, but 

 without differentiation of content into egg and periplasm; the other 

 serving as the supplying gametange, antherid (Conidiobolus utriculosus, 

 Basidiobolus ranarum, Dispira americana Thaxter, 1895, Endogone 

 lactiflua, etc.). 



3. The progressive tendency shown in the germination, or out- 

 growth, of the young zygote immediately after fusion from the copu- 

 lation point, or from one of the gametangia, the ripe zygote being formed 

 outside the gametangia, not within them according to the typical 

 process. The tendencies in this direction appear at different levels 

 in the zygomycete alliance. Examples are PiptocephaUs freseniana, 



® The following forms among the phycomycetes have been suggested as proto- 

 types of the ascomycetes. The Peronosporales by de Bary (1881) for the usual 

 ascomycete type, PiptocephaUs for the Eremascus type; Myzocytium and Protascus 

 by Dangeard (1903-06, 1910), Cystopiis by Lotsy (1907) and Monoblepharis by 

 Nienburg (1914). 



