4 BOTANICAL GAZETTE [jxjly 



to roll inward so closely that the edge of the pileus becomes pressed 

 against the loosely interwoven ends of the filaments covering the 

 stem. Figs. 8 and 32 show a fruit in this condition with the ends 

 of the filaments of the pileus and those of the stem intermingled. 

 It is this condition that caused the uncertainty in the examination 

 of young forms as to whether the hymenophore was endogenous 

 or exogenous in origin. 



The development just described reminds one of Hartig's (16) 

 description of the development of Armillaria niellea. He found 

 that the hymenophore developed exogenously at first, and that 

 later by epinastic growth the margin of the pileus became incurved, 

 and that the marginal veil developed from the interweaving of 

 filaments growing from the margin of the pileus with similar ones 

 growing out from the stem. This course of development, however, 

 has been shown by Beer (id) and Atkinson (5) not to be correct 

 for Armillaria mellea. Blizzard (ii) in his studies on exogenous 

 forms found the pileus in several to be strongly incurved, but he 

 did not report an interlacing of filaments from the pileus and stipe. 

 At this stage of development the strong epinastic development 

 ceases and the expansion of the pileus takes place more uniformly 

 in all directions (figs. 9, 12, 15, 19, 23). 



During the changes in the form of the pileus just described the 

 general relations of hymenophore to stipe and pileus remain the 

 same as seen in the younger stages (figs. 29, 30), but the palisade 

 layer becomes more and more arched (fig. 32). The space between 

 the arched hymenophore is lined with the uniform terete ends of the 

 filaments of which the palisade layer is composed. 



ORIGIN AND EARLY DEVELOPMENT OE LAMELLAE 



Figs. 9-1 1 show low magnification of median and tangential 

 longitudinal sections of a young fruit body in which the first trace 

 of gill development is distinguishable. The location of these sec- 

 tions is shown in text fig. lA , while the small arrows in text fig. iB 

 show the direction of growth in the hymenophore at this time. The 

 gill salients arise as folds occurring in the angle between the stem 

 and pileus where the palisade layer is first developed. The stem 

 is narrower in the region of the developing hymenophore than below 



