652 THE PHYLOGENY OF THE FUNGI 



at whose tips they stand symmetrically perched. Frequently the sterigma 

 breaks at some distance below the spore and remains attached to it like a 

 handle. The spore fruits vary in simplicity or complexity of structure from 

 very small bodies with a single closed hymenial cavity as in Protogaster up 

 to the very complex structures with a columella which may be extended 

 into a stalk as in Secotium, Podaxis, Battarrea, etc. Some remain closed 

 until some accident (decay, attack by insects, etc.) breaks them open and 

 permits the spores to escape, others provide definite modes of spore- 

 escape, e.g., Lycoperdaceae, Sphaerobolaceae, Phallaceae, etc. Yet in all 

 cases the spores are mature before they can escape and are symmetrically 

 attached to the sterigmata. Yet aside from these differences there are 

 many points of structural similarity, as pointed out in Chapter 15, 

 between some Gasteromyceteae and some Agaricaceae. Russula and 

 Lactarius have anatomical features and spore markings and chemical re- 

 actions very much like Elasmomyces, so that their close relationship can 

 be assumed unless we surmise this to be a case of convergent evolution. 



Origin of Agaricales 



Singer (1950), in a chapter entitled " Phylogenetic theories concerning 

 the origin of the Agaricales," discusses three hypotheses that have been 

 proposed to explain the origin of this order: (1) they are directly and 

 wholly derived from the Aphyllophorales (Polyporales) ; (2) they are 

 directly and wholly derived from the Gasteromyceteae, probably along 

 several lines; (3) they are partly derived from the Polyporales and partly 

 from the Gasteromyceteae. He, himself, is in favor of the second hypoth- 

 esis but his explanations of the other two are good. Taking these hypoth- 

 eses in turn the author will give a resume of the facts that stand in favor 

 of and against each one. 



Singer^ s Hypothesis No. 1 



Agaricales Derived Wholly from Polyporales. This is perhaps the 

 oldest theory since the time that the idea of evolution began to affect the 

 classification of fungi. Briefly sketched, it assumes that from a simple 

 resupinate spore fruit with a smooth, or possibly rather loose, cottony, 

 hymenium, evolution progressed toward more compact structures some 

 of which assumed a lateral position or even became stipitate. These forms 

 with flat hymenium made up the old family Thelephoraceae. The amount 

 of hymenial surface in proportion to the size of the spore fruit was limited, 

 so long as the hymenium was a plane surface. This surface became in- 

 creased by the formation of hymenium-covered pegs or teeth projecting 

 from the surface, leading to the Hydnaccae. In a slightly different manner 

 the surface became increased by a reticulate pattern of outgrowth so that 

 eventually there were very numerous pits or pores of various depths, lined 



