48 KANSAS UNIVERSITY SCIENCE BULLETIN. 



of the stomata shows that the smaller the stoma the relatively 

 longer are the free-moving walls of the guard cells, so that 

 the leverage is increased. Other parts of the mechanism of 

 the gramineous type of stoma have been explained by other 

 investigators. 



In the very young leaf the stomata are not of the gramineous 

 type, but are modified as the leaf matures. In the preserved 

 material of the young leaf the stomata stand open, while they 

 are never found open in the preserved material in the mature 

 leaves. (Figs. 20 to 22.) 



LOWER EPIDERMIS. 



Aside from the stomata, the lower epidermis showed char- 

 acteristic differences. As noted above, the cell walls of No. 1 

 were so thin as readily to distinguish it from the others, and 

 the cells were also much smaller. No. 4 could be easily detected 

 by its relatively large cells with wavy walls, while the walls 

 of the other three were straight. The average area of the 

 lower epidermal cells was as follows: No. 1, .000108 sq. mm.; 

 No. 2, .000142 sq. mm. ; No. 3, .000147 sq. mm. ; No. 4, .0002°, 

 sq. mm. (Figs. 45 to 48, sec. D.) 



EPIDERMAL HAIRS. 



The number and character of the epidermal hairs are dis- 

 tinguishing features. No. 1 has 55 stellate hairs to the sq. mm., 

 with 5 to 9 branches to a hair. They are small and very thin 

 walled. No. 2 has 70 stellate hairs per sq. mm., with from 4 to 

 9 branches, and the hairs are generally long and thick walled. 

 No. 3 has 215 stellate hairs per sq. mm., with 6 to 14 branches 

 on each hair. These almost completely cover the surface of 

 the leaf and make immediately distinguishable the smallest 

 section of a leaf. The hairs of No. 3 are generally shorter and 

 thicker walled than in No. 2. No. 4 has 80 hairs per sq. mm., 

 with from 6 to 10 branches on each hair. Except in thickness 

 of wall, they are like those of No. 2, but the walls are much 

 heavier, having the central cavity a mere line. (Figs. 45 to 48, 

 sec. E.) 



UPPER EPIDERMIS. 



The cells of the upper epidermis of the several oaks differed 

 in size and thickness of walls. No. 1 had the thickest walls. 

 The walls of No. 4 were nearly as heavy, while those of No. 2 

 were lightest. Comparative average area of upper epidermal 



