38 
GERTRUDE E. DOUGLAS 
satisfactory, the freezing apparently not affecting the buttons. After 
washing and dehydrating they were cleared in cedar oil and embedded 
in 52° paraffine. Sections were cut from 5-7 microns in diameter 
and stained with fuchsin. 
Early Stages in the Development of the Fruit Body. — It was possible 
to obtain in this manner fruit bodies in which no differentiation had 
taken place. A longitudinal section of a young button, about 2 mm. 
in diameter, is shown in figure i, attached to the base of a more de- 
veloped plant. It consists of homogeneous tissue, composed of small, 
densely interwoven hyphae, about 1 fx \n diameter. The external 
hyphae are somewhat larger (1.5 /x) and take the stain more readily. 
Later the young fruit body becomes somewhat flask-shaped, as shown 
by the section of the larger plant in figure I . The interwoven hyphae 
assume a generally longitudinal direction throughout the center of 
the fruit body, but all over the surface they already exhibit a strong 
inclination to turn outward. At the apex this epinastic tendency has 
resulted in a differentiation into two regions, the pileus and stem 
primordia, separated by an annular constriction or furrow. The 
tissues of both regions, however, are still homogeneous, that of the 
upper, in fact, being made up of the extension of the hyphae of the 
lower. 
Differentiation of the Primordium of the Hymenophore. — As the 
basidiocarp increases in size, the differentiation between the stem 
and pileus fundaments becomes more marked (fig. 2). As yet there 
is no distinguishable hymenophore fundament, although a slightly 
increased staining capacity of the hyphae in the furrow suggests that 
a rapid growth is taking place at this point. The elements are still 
similar to those which are characteristic of the margin of the pileus, 
broad (1.6-3.5 jj. in diam.), and blunt at the ends (fig. 19). Very soon 
the typical hymenophore elements appear. They are slender and 
sharply pointed at first, as they are in many of the endogenous forms. 
They branch off very profusely from the subadjacent tissue of the 
pileus and are stained more deeply (figs. 3, 4, 5, 22). 
Development of the Palisade Layer. — The dense crowding of these 
elements causes them to become organized very soon into a palisade 
layer. In figure 22, an enlargement of figure 5, we may observe that 
the under surface of this zone of very active growth is still somewhat 
irregular, due to the varying lengths of the narrow-pointed hyphae. 
Later they become more even and blunt and the fruit body presents 
