19IS.] DEVELOPMENT OF AGARICUS RODMANI. 343 



PLATE XL 



Figs. 17-19 and 21-23, all from a single basidiocarp (No. %), from selected 

 serial sections parallel with the axis of the stem and " tangential " in the pileus. 

 Fig. 17 is from near the stem, and shows the three stages of the developing 

 hymenophore, primordial zone, level palisade zone, and the zone of gill sa- 

 lients (transected) with different stages in the origin of the latter from the 

 level palisade condition (see text for details). The general annular cavity- 

 is well shown. 



Fig. 18. More highly magnified view of portion of the same section 

 in the region of the origin of the gill salients from the level palisade stage. 



Fig. 19. More highly magnified view of the young gill salients, showing 

 how they flare, or fantail, when released from the pressure to which the 

 elements are subjected in the level palisade zone, also showing how this 

 flaring of the young gill salients crowds the intervening palisade cells of 

 the original level into " ridges," these ridges of palisade in the notch between 

 two lamellae being formed later than the gill salients, and as a result of the 

 lateral pressure of the flaring salients. For details see the text. 



Fig. 20. (No. %.) Section from another basidiocarp showing transi- 

 tion from the level palisade stage to the gill salients. 



Fig. 21. Section nearer the margin of the pileus than that shown in Fig. 

 17. In the middle area the gill salients are cut near their distal end where 

 they are very low (see text for details). Transition to level palisade and 

 primordial zone on either side. 



Fig. 22. Section still nearer the margin of the pileus showing the level 

 palisade zone in the center, and the primordial zone on either side. 



Fig. 23. Section still nearer the margin of the pileus, entirely through 

 the primordial zone. 



PLATE XIL 



Figs. 24-31. Selected serial sections from a single basidiocarp (No. Ys), 

 parallel with the stem axis and from nearly median in the stem to mid- 

 way from stem surface to the margin of the pileus. Here the hymenophore 

 extends for some distance down on the outward sloping surface of the stem 

 fundament, and there are little " stalls " or pigeon holes between them in 

 the angle at junction of pileus and stem. See text for details. 



PLATE XIIL 



Figs. 32-42. Selected serial sections from a single basidiocarp (No. 11), 

 parallel with the axis of the stem and from median in the stem to " tangen- 

 tial " in the margin of the pileus. See text for details. 



PROC. AMER. PHIL. SOC, LIV. 2I9 W, PRINTED SEPT. 8, I915. 



