312 ATKINSON— MORPHOLOGY AND [April 23, 



giving rise to the teleoblem, or finished volva. But in the genus 

 Agaricits'^ no such cleavage layer is formed, and the surface of the 

 pileus primordium becomes consolidated with the blematogen layer 

 which here does not form a true volva, or teleoblem. 



The lower limb of the annulus of Agaricus rodmani is not, there- 

 fore, strictly, homologous with the volva of the Amanitas, not even 

 including the thin layer of the stem and pileus which sometimes tends 

 to peel off, since it does not comprise all of the blematogen layer, 

 nor is it separated from the pileus by a distinct cleavage layer. If it 

 were homologous with the volva of the Amanitas, then this species 

 would represent a generic type distinct from Agaricus (Psalliota) . 

 In fact other species of Agaricus frequently show a similar condi- 

 tion of the annulus, i. e., where the margin is " grooved," due to the 

 inset of the pileus margin into the veil where the conditions for the 

 robust development of the veil are favorable. In Agaricus campes- 

 tris the annulus frequenlty presents a grooved margin, not only in 

 the case of cultivated forms, but more rarely in the feral state. 

 This condition is well shown in Plates 11 and 12 of my article on 

 Agaricus campestris.^ In Fig. 20 of that article the lower limb of 

 the annulus has broken away from the outer surface of the incurved 

 pileus margin, while the upper limb is still attached to the edge of 

 the pileus. In Figs. 18 and 19 the upper limb has also become freed 

 from the pileus margin and the grooved character of the edge of the 

 annulus is very distinctly shown. In Fig. 15 of the same article, 

 sections of the young basidiocarps show very clearly the position of 

 the lower limb of the annulus extending over the outer (upper) 

 side of the pileus margin. Fig. 20 also shows very clearly that the 

 annulus as a whole is ripped off from the lower part of the stem, 

 being an exaggerated case of the slight peeling up of the thin surface 

 layer of the stem mentioned above in Agaricus rodmani. That the 



* Atkinson, Geo. F., "The Development of Agaricus arvensis and A. 

 comtulus," Am. Jour. Bot., 1, 3-22, pis. i, 2, 1914. 



Atkinson, Geo. F., " Homology of the Universal Veil in Agaricus," Myc. 

 Centralb., 5, 13-19, pis. 1-3, 1914. 



Atkinson, Geo. F., " The Development of Lepiota clypeolaria, Ann. Myc, 

 12, 346-356, pis. 13-16, 1914. 



s Atkinson, Geo. F., "The Development of Agaricus campestris," Bot. 

 Gaz., 42 : 241-264, pis. 7-12, 1906. 



