1915-] DEVELOPMENT OF AGARICUS RODMANI. 323 



Organisation of the Pilous. — The organization of the pileus be- 

 gins in connection with the primordial hymenophore zone. The 

 upper part of this zone is very probably to be regarded as the primor- 

 dium of the pileus margin which then increases by centrifugal 

 growth. It is marked from an early period by strong epinastic 

 growth, so the margin becomes strikingly involute, a feature also 

 characteristic of Agaricus canipestris/^ A. arvensis,^^ A. comtulus, 

 etc., as I have earlier described. The general relation of the hyphse 

 in the primordium of the pileus margin is a parallel one, and they 

 become more and more strongly incurved as a result of epinasty. 

 As the pileus primordium increases in width by marginal growth, it 

 also increases in thickness, more perceptibly so farther back from 

 the margin where the new growth is older. In this way the organi- 

 zation of the pileus advances more and more into the outer zone of 

 the ground tissue, the blematogen, and becomes consolidated with it."' 



Organisation of the Stem. — The stem area is delimited at the 

 same time as the pileus area b}^ the origin of the young hymenophore 

 zone, but its organization and differentiation from the ground tissue 

 seems to lag behind the early stages of the organization of the pileus 

 margin. While a general and more or less diffuse growth and ex- 

 pansion occurs for some time in the stem area, the first evidence of a 

 differentiation from the ground tissue is seen in the organization 

 of the stem surface. The outline of the stem may be compared to 

 that of a broad, flat cone, since the stem at first is very short and 



2* Atkinson, Geo. F., "The Development of Arnanitopsis vaginata," Ann. 

 Myc, 12, 369-392, pis. 17-19, 1914. 



25 Atkinson, Geo. F., " The Development of Agaricns campestris," Bot. 

 Gas., 42: 241-264, pis. 7-12, 1906 (see figures 11 and 12). 



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

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



-~ In Agaricus campestris var. edulis, Vittadini (" Fun. Mang.," 44, pi. 

 6, fig. I, 1835) in a young oval fruit body, figures and describes the outline 

 of the pileus within a stout volva, and states that, during the course of 

 development, the volva is ruptured circularly, and the margin of the pileus 

 as it emerges is held for a time against the stem by the lower limb of the 

 annulus. His account of the release of the volva (blematogen) from 

 the pileus does not seem clear, and his figures do not show the transition 

 stage from a to & in figure i of his Plate VI In Agaricus rodinani nor in 

 any other species of Agaricus (Psalliota) have I ever seen any indication of 

 the clear cut outline of the pileus surface as distinct from the blematogen, 

 such as Vittadini shows at a, fig. i. 



