﻿BOTANICAL GAZETTE 



first, and this indicates that the primordia of hymenophore and 

 pileus margin may arise from a fundament common to both. The 

 further organization of the pileus consists in the growth of new 

 elements, as well as in the incorporation of the elements of the inner 

 zone of radial hyphae. 



At the stage represented in fig. i there is no evidence either 

 of an annular gill cavity or of the fundaments of the lamellae. The 

 next stage in the differentiation of the basidiocarp is the appear- 

 ance of a general, annular, prelamellar cavity. This is formed as 

 a result of tensions due to unequal growth. The more rapid growth 

 and expansion of the pileus fundament and the more rapid elonga- 

 tion of the stem fundament next the pileus bring into strong tension 

 the less rapidly growing tissue in the angle between the pileus and 

 the upper part of the stem, so that this tissue is torn apart. Prior to 

 and at the time this tearing apart of the tissue occurs, the hyphae 

 of the lower part of the pileus fundament are growing down- 

 ward. When the rift first takes place the dome of this cavity, 

 that is, the under surface of the exposed pileus fundament, is very 

 irregular and ' ' frazzled" from the numerous loose hyphae which 

 project downward into the cavity, exactly as described for 

 Agaricus campestris by the writer (Atkinson 5). The lower 

 surface of the cavity also presents in its early formation numerous 

 loose hyphae on the surface of the stem and fundament of the 

 partial veil. 



The more active growth of the pileus, where the hyphae are 

 richer in protoplasmic content and stain more deeply, is at some 

 distance from the stem, near the outer portion of the annular cavity. 

 It is along this under surface of the pileus that the palisade layer 

 is first formed as the dome of the cavity smooths out and acquires 

 a more even contour. At the extreme outer margin of the cavity, 

 however, the surface is still irregular, due to the fact that the forma- 

 tion of the cavity and the organization of the palisade layer on the 

 under surface of its roof are centrifugal, thus following up the 

 centrifugal growth and extension of the pileus margin. The 

 elements, therefore, not only of the pileus but also of the young 

 hymenophore, are younger toward the margin of the pileus because 

 of this centrifugal order of development. 



