[VOL. 2 

 364 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



PROVISIONAL AKRANGEMENT OF MAIN LINES OF DEVELOPMENT IN 



ASCOMYCETES 



For those who are interested in the suggestions as to the 

 phylogeny and relationships of the Ascomycetes presented in 

 this paper, a diagrammatic arrangement of the principal 

 series or lines which will illustrate the relationships tenta- 

 tively held by the writer may be acceptable. It is with con- 

 siderable hesitation that this arrangement is presented. The 

 writer trusts that it will be accepted as provisional and in 

 the nature of a working hypothesis which he hopes will fur- 

 ther stimulate investigation, suggestions and criticisms on 

 the ideas embodied in this paper, all of which, for or against, 

 will be gladly welcomed. 



Dipodascus, a primitive form, cells of mycelium polyen- 

 ergid, gametogenous branches large, unequal, polyenergid. 

 Ascus is elongated, broadened zygospore, zygote germinating 

 immediately forming a broad germ tube in which spores are 

 formed. Since the process does not go on to the formation 

 of a sporangium, a different mode of internal free cell-forma- 

 tion then arose in connection with the precocious formation of 

 spores in the zygote and retention of epiplasm which assists 

 in discharge of spores. Dipodascus retains tendency of 

 gamogenic branches to copulate early before they become 

 strongly differentiated as gametangia, just as in Mucorales. 



I. Protoascomycetes are derived by descent and degenera- 

 tion from some such primitive ascomycete form as Dipodascus. 

 The ascus when of sexual origin is the zygote, except in Nad- 

 sonia. 



Endomyces Magnusii is the nearest known form to the gen- 

 eralized condition seen in Dipodascus. Cells of mycelium 

 usually polyenergid, those of stout mycelium are polyenergid. 

 Formation of ascus in Endomyces Magnusii repeats formation 

 of zygospore in Zygorhynchus. Gamete branches in both are 

 multinucleate, but when cell wall is laid down delimiting the 

 gametangia all but one nucleus in each gametangium of E. 

 Magnusii are excluded. After contact of the two sexual 

 branches the male gametangium is formed by enlargement of 

 its tip, into which protoplasm and the one nucleus migrates, 



