272 KANSAS UNIVERSITY SCIENCE BULLETIN. 



THE LEAF. 



The gross structure of the leaves is quite different in each 

 of these oaks. The leaf of Q. rubra is somewhat smaller than 

 either of the others, has a smooth upper surface and a dark 

 green color. It is not so deeply lobed as the others and is less 

 flexible. The leaf of Q. schneckii is of a light green color and 

 quite deeply lobed, and the lobes are more divided into smaller 

 lobes than any of the others. It is much thinner and hence 

 more flexible than any of the others. The leaf of Q. coccinea 

 is of a dark green color with a glossy upper surface. It is 

 longer than the others and has fewer lobes, which are nearer 

 at right angles to the midrib than in any of the others. Q. 

 macrocarpa has a leaf quite different from any of the others. 

 It is of a light green color and has many hairs on the lower 

 side. The young leaves of all these oaks have hairs on both 

 the upper and lower surfaces. The comparative sizes and 

 shapes are shown in figures 1, 2, 3 and 4. 



The Bleached Leaf. 

 One of the first differences noticed between the leaves of the 

 different oaks was the time required to bleach the leaves. The 

 leaf of Q. macrocarpa was cleared in the chloral hydrate in 

 about two days, and took about the same time to clear in the 

 potassium hydrate. The leaf of Q. schneckii and Q. coccinea 

 was cleared in the chloral hydrate in about five days and in 

 the potassium hydrate in two days. The leaf of Q. rubra was 

 cleared in the chloral hydrate in seven days and in the potas- 

 sium hydrate in three days, thus taking about twice as long to 

 bleach as it took to bleach the leaf of Q. macrocarpa. The 

 venation of the leaves was examined in the bleached leaves, 

 but no constant difference could be noticed. 



Upper Epidermis. 



There is a noticeable difference in the size of the upper epi- 

 dermal cells. There being 2500 cells per square millimeter in 

 the leaf of Q. macrocarpa, 1900 in the leaf of Q. schneckii and 

 Q. coccinea, and about 1650 cells per square millimeter in Q. 

 rubra; the greatest difference being between Q. macrocarpa 

 and the others, thus easily distinguishing Q. macrocarpa from 

 the others. (See figs. 5, 6, 7 and 8.) A cross section of the 

 leaf shows the upper epidermis of Q. ruba to be the thickest, 

 being about .03 mm. thick. The upper epidermis is about .028 



