I9IS-] DEVELOPMENT OF AGARICUS RODMANI. 329 



Relation of the Hymenophore to the Stem. — One of the taxo- 

 nomic characters employed for the genus Agaricus (Psalliota) is the 

 free condition of the gills from the stem. In Agaricus campestris, 

 while the gills are usually free, they are close to the stem, and in 

 some cases are even adnexed to the stem. The same is true of 

 Agaricus rodinani. Peck^- says of the lamellae, — " free, reaching 

 nearly or quite to the stem. It is possible that in some examples 

 the gills may be broadly attached to the stem fundament at the time 

 of their origin, but become free at maturity by changes in the relation 

 and tensions of the parts during expansion of the plant. That the 

 young lamellse are sometimes broadly attached around the upper end 

 of the stem fundament has been observed in a number of examples 

 during this study of development. In some examples the attach- 

 ment of the stem is very broad, in others slight, and in still others 

 the lamellae are free from the time of their origin. 



Deceptive Appearance of Sections near the Stem zvhen the Young 

 Lamella- are Attached. — In studying the origin of the lamellae in 

 plants where the hymenophore, from its earhest appearance, is en- 

 tirely free from the stem, little difficulty is experienced in the in- 

 terpretation of the situation presented, in case there is a fairly well 

 formed annular cavity prior to the origin of the gill salients. 

 Longitudinal sections next the stem then present the simple situation 

 shown in Fig. 17. But in those cases where the hymenophore 

 primordium extends downward on the outer surface of the stem 

 apex, as shown in Figs. 11 and 12, sections passing from the stem 

 through this portion of the hymenophore, after the origin of the gill 

 salients, present a complicated structure, which may be very con- 

 fusing unless all the features of the situation are taken into con- 

 sideration. As stated above the stem axis of the sections from which 

 Figs. II and 12 were made is parallel with the longitudinal direction 

 of the plate. In very young basidiocarps; as already described, the 

 stem surface slopes outward at a very strong angle as shown in 

 Fig. 32. 



Now, when the gill salients begin to form by downward, or out- 

 ward, extension of the level palisade, in those cases where the 

 hymenophore primordium extends down on the surface of the stem, 



32 Peck, C. H., N. Y. State Mus. Nat. Hist Rept., 36, 45, 1885. 



