THE DEVELOPMENT OF SOME SPECIES OF AGARICS 225 
Simultaneously with this, subadjacent hyphae along radial areas 
corresponding with the gill areas, by elongation, push their way down- 
ward and govern the origin of the gill salients. Figures 24 and 25 
show this feature in excellent detail. These down-growing salients 
of the level palisade layer are the first evidence of the appearance of the 
lamellae. Continued growth of these salients produces the lamellae, 
as observed in species of Agaricus (i, 2, 4), Coprinus (5), Cortinarius 
(10), etc. 
The subhymenial hyphae are branched in a corymbose manner^ 
Figure 27, and supply new elements within the hymenophore layer. 
Figure 28 is a higher magnification of a portion of Figure 27 and shows 
in detail the corymbose branching. 
Growth in width of the lamellae occurs by the further elongation 
of the tramal hyphae which branch as above described. These new 
elements are interpolated between the older hyphae at the edge of the 
gill. 
The development of the lamellae is centrifugal as are the structures 
preceding their origin. Therefore the oldest portions of the lamellae 
are nearest the stipe and proceed in a radial direction to the margin. 
Since the margin of the pileus is involute, a tangential section through 
that portion of the fruit body parallel with the axis of the stipe will 
present an appearance as represented by Figure 16. Below, it shows 
a portion of the inroUed pileus edge. This relation of the gills to the 
involute margin of the pileus has been adequately described by Atkin- 
son for Agaricus rodmani (4). 
Structure of Stipe and Pileus. — As the basidiocarp grows the stipe 
becomes even in diameter. This results largely from the elongation 
of the peripheral hyphae and more abundant branching in the upper 
portion 'of the stipe, together with the enlargem.ent of the cellular 
elements. The process is a gradual one, as Figures 3-9 show. 
The pileus at the same time increases in all its dimensions and 
becomes more expanded (Fig. 10). The general direction of its ele- 
ments is horizontal and radial (Fig. 29). Those on the surface are 
more closely interwoven, and this serves to produce a smooth surface. 
Figure 30 is a high magnification of a portion of the pileus which shows 
this structure very clearly. The hyphal cells have very firm walls 
and are exceedingly large, measuring 7 to 8/x in diameter. 
