216 BOTANICAL GAZETTE [September 



As has been shown, the pileus begins its development at the stem 

 and gradually extends its organization into the hymenophore 

 primordium at the margin of the pileus (fig. 67). Growth con- 

 tinues to be centrifugal. The gill ridges start to develop at the 

 stem in regular spaced areas and radiate outward toward the 

 margin. On account of the very great density of the palisade 

 elements and the continuous addition of new fibers by branching 

 of the palisade elements, the surface of the latter is soon thrown 

 out into folds (figs. 18, 38, 66). Multiplication of hyphae never- 

 theless continues to go on, and with it certain elements in the layer 

 subjacent now begin to elongate rapidly and to carry downward 

 the much crowded palisade layer. Since the grow r th of these 

 young salients begins at the stem, the gills elongate first in this 

 region. Passing outward the ridges become less developed until 

 they disappear in the even palisade surface (figs. 7-10, 26-30, 

 42-46, 56-60, 67). Elongation of the elements of the trama con- 

 tinues while the ridges are progressing outward until mature gills, 

 extending from the stem to the pileus margin, are fully developed. 

 As these radiating rows get farther and farther apart, secondary 

 gills form in the same manner between them. Before the basidia 

 mature, certain elements of the palisade layer pubh out very rapidly 

 and form cystidia (figs. 49, 68, 69), the nucleus of one of which 

 shows plainly in fig. 49. Successive stages in the development of 

 young gill salients are shown in the high-power photographs of /. 

 entheloides (figs. 50-52). Occasionally the gill cavity is strongly 

 arched, 3 and the development of the ridges appears to begin on 

 the stem, a circumstance which brings about appearances such as 

 are shown in figs. 43 and 44 in sections cut parallel to the medium 

 axis. In consequence the salients here are cut nearly perpendicular 

 to their direction of growth, and the gill cavity which extends in 

 between them appears as a series of little pockets. A similar 

 appearance at the margin is often caused by cutting perpendicular 

 to the salients on the enrolled edge of the pileus (figs. 14, 15, 34, 64). 

 The development of these plants was not carried beyond the stages 

 represented in figs. 49, 68, and 79, in which well developed cystidia, 



3 See Atkinson (6, 7) for a complete explanation of these appearances. 



