SEXUAL REPRODUCTION 67 



of reproduction following the sequence of differentiation ; 

 commencing in the earliest group, the Phycomycetes, con- 

 tinued to a greater extent in the Ascomycetes, and entirely 

 absent from the most modern group, the Basidiomycetes. 



From the present standpoint of knowledge Brefeld's 

 scheme of evolution of the fungi is not generally accepted 

 for the following reasons. In the Saprolegnieae, Perono- 

 sporaceae, and some other groups belonging to the Phy- 

 comycetes, the sexual organs consist of an antheridium 

 and an oogonium, which are homologous with the sexual 

 organs of Vaucheria, an alga considered by some as re- 

 presenting the group of algae from which the fungi 

 descended. 



In the Mucorineae, another group included in the 

 Phycomycetes, the sexual organs consist of two specialised 

 portions of hyphae called gametes. By the union and 

 fusion of the contents of two progametes a zygospore 

 is formed. Perhaps these gametes are but modifications 

 of the antheridium and oogonium of the older groups, 

 Peronosporeae, etc. In some species the two gametes 

 differ in size and other respects ; in others the two gametes 

 are at all events morphologically similar. 



In some Ascomycetes antheridia and oogonia are still 

 present, and of functional value, in widely separated groups. 

 There is also present in the Ascomycetes a second type of 

 sexual reproduction, in which the receptive cell, the equiva- 



of growth ; 3, conidial fruit on a larger scale ; 4, a single cluster of conidial 

 fruit or sporangia, showing the rhizoids or vegetative hyphae at the base ; 

 5, optical section of a sporangium : a, columella : b, sporangial sac filled 

 with spores (technically conidia) ; 6, spores from sporangium, some germi- 

 nating ; 7, spores on a larger scale to show markings on epispore ; 8, mature 

 zygospore, the suspensors are indicated ; 9, mycelium running between 

 cells of bulb containing starch. Figs, i and 2, nat. size ; rest mag. 



