BOT.-VOL. II.] PEIRCE-SEQUOIA SEMPERVIRENS. 93 



being located at the ends. The upper surface of the leaf is 

 convex, the lower concave, the upper surface and the edges 

 being greatly strengthened by the thickened and heavily 

 cutinized walls of the epidermal cells and by the underlying 

 single layer of sclerenchyma. Beneath this is the very per- 

 fectly developed palisade parenchyma, extending from edge 

 to edge of the leaf. The remainder of the mesophyll is com- 

 posed of simple, unbranched parenchyma, enclosing many 

 intercellular spaces, and bounded on the under side of the 

 leaf by the single layer of fairly thick-walled epidermal cells. 

 In contrast to this, fig. 2, a similar diagrammatic view of 

 the cross-section of a larger white leaf shows a less convex 

 upper, a less concave lower, surface, and the almost or quite 

 complete absence of sclerenchyma cells except at the edges 

 of the leaf (see fig. 9). The most striking difference in 

 the structure of the two leaves, however, consists in the 

 complete absence of palisade parenchyma from the white 

 redwood leaf. The remainder of the mesophyll is com- 

 posed of somewhat larger parenchyma cells than in the 

 green leaves, and the intercellular spaces are also slightly 

 larger. 



Examination of these cross-sections under higher magni- 

 fication (figs. 7-10) reveals still more plainly the contrast 

 between the white and the green leaves. Figure 7 is a 

 detail from near the middle of the green leaf represented 

 in fig. I. Figure 7 shows the thick-walled epidermal, the 

 thicker walled sclerenchyma, cells, and the regular palisade- 

 parenchyma cells. These contain many chloroplastids, 

 slightly larger than the starch-grains indicated in the figure. 

 There are many of these starch-grains imbedded in the 

 cytoplasm. Vacuoles are numerous, and evident. The 

 cytoplasm and nucleus are sharply differentiated. Figure 

 8 represents the corner of fig. i cut off by the dotted Hne. 

 In fig. 8 are shown the very strong sclerenchyma cells im- 

 mediately underlying the epidermis at the edge of the leaf, 

 and extending almost continuously along the under side to 

 and around the resin-tube. This last is large and bounded 

 by many suitably supported, thin-walled, glandular cells. 



