Box— Vol. II.] PEIRCE— SEQUOIA SEMPERVIRENS. 97 



Other differences in structure between the white and the 

 green leaves of redwood may be mentioned. As shown by 

 figs. II, 12 and 13, the walls of the epidermal cells of the 

 white are not as thick as those of the green leaves. Figure 

 II shows the epidermal cells around and above the some- 

 what depressed stoma on a white leaf. Figure 13 is a similar 

 view of a part of the surface of a green leaf. Both figures 

 are of a stoma from the upper surface. Though in the green 

 and in the white the mouth of the stoma is about equal in 

 size, the adjacent epidermal cells are smaller as well as thin- 

 ner walled in the white redwood. Figure 12 represents the 

 guard-cells of the stoma, only the upper part of which is 

 shown in fig. 11. There are no chromatophores in the 

 guard-cells, but the nuclei are well differentiated. 



Though the numbers of stomata on the under side of the 

 green and the white leaves are about equal, there are more 

 stomata on the upper surface of the white leaves than of the 

 green. Figures 3 and 4 represent very diagrammatically 

 the shape and size, but exactly the numbers, of the stomata 

 in equal areas of epidermis from the upper side near the 

 midrib of a green and of a white leaf from redwoods in the 

 Santa Cruz Mountains. Figure 5 indicates the number of 

 stomata in an equal length of epidermis similarly situated 

 but from a green leaf from one of the redwoods in the 

 Arboretum of Stanford University. Figure 6 is another 

 strip from a white redwood leaf from the mountains. Two 

 facts are demonstrated by these figures : first, that the white 

 leaves always have more stomata on the upper side than do 

 the green ones; second, that in the green leaves the number 

 of stomata on the upper side of the leaf is proportioned to the 

 humidity of the region in which the tree grows. The sec- 

 ond is a fact well known and understood; the first is new 

 and not easy to understand. In all probabihty it will be 

 found that the white redwoods occur where transpiration is 

 not so great as in many places in the mountains where green 

 redwoods occur. In a thicket there would evidently be less 

 rapid transpiration than in the open at one side or above the 

 thicket. The white redwood suckers which I have seen are 



