328 ATKINSON— MORPHOLOGY AND [April 23, 



trate also the relations now under consideration). An examination 

 of the relation of line 4, in diagram 6, to the gill salients, the palisade 

 and primordial areas, will assist in making the relation of the phases 

 of the hymenophore presented in Fig. 17 very clear. 



In the middle of the figure, or section, the gill salients are cut 

 transversely. On either side of the middle they are cut obliquely, 

 the more so the nearer the palisade area the salients are cut. But 

 when the gill is so young, the structure of an oblique section at this 

 angle is practically the same as in a transection. Since the hymeno- 

 phore is older next the stem, and progressively younger toward the 

 margin of the pileus, the gill salients are older next the stem, and 

 younger next the palisade area, where they are very low and grade 

 off insensibly into the level palisade zone. Tov/ard the left and right 

 from the middle of such a section as is represented by Fig. 17, the 

 salients become less and less prominent until they grade insensibly 

 into the level palisade zone on either side. In like manner the 

 palisade zone grades to the left and right into the primordial zone, 

 and this into the margin of the pileus, showing practically the same 

 relation, so far as the palisade and primordial zones are concerned, as 

 in a radial section. 



Fig. 21 is from a section made near the outer ends of the middle 

 salients, about in the region represented by line 7 in diagram 6. 

 Only a few salients are shown, these are very low, and on either side 

 soon grade insensibly into the palisade zone. Fig. 22 is from a 

 section made in the region indicated by line 8 in diagram 6. Here 

 there are no gill salients (nor any evidence of ridges in the hymeno- 

 phore), a broad area in the middle is the palisade area, and this 

 grades on either side insensibly into the primoridal area. Fig. 23 is 

 from a section made in the region indicated by line 9 in diagram 6. 

 It is entirely within the primordial zone, near the margin of the 

 pileus. Knowing this relation of the different phases of the hymeno- 

 phore, one can observe the transition of the primordial phase into the 

 level palisade phase, and this into the phase of the salients. In 

 other words, one can study the method of origin of the lamellae by a 

 study of the different phases of the gill salients in the area of transi- 

 tion from the palisade zone into the zone of the young gills. 



