274 KANSAS UNIVERSITY SCIENCE BULLETIN. 



than in any of the others. The length of the opening is nearly 

 one-half the length of the guard cells in Q. schneckii, about 

 two-fifths the length of the guard cells in Q. rubra and Q. 

 coccinea and one-third the length of the guard cells in Q. 

 macrocarpa. The length of the larger stomata of Q. schneckii 

 is about .03 mm., and the length of the smaller sized stomata 

 of Q. schneckii is about the same as the length of the stomata 

 of Q. rubra and Q. coccinea, which is about .024 mm. In Q. 

 macrocarpa the stomata are about .023 mm. long but are much 

 narrower than in the others, hence they look much smaller. 

 The proportionate lengths and shapes are shown in figures 

 9, 10, 11, 12. 



Leaf Cross-section. 



In the cross-section of the leaves it is noticed that the leaf 

 of Q. rubra is slightly thicker than the others, it being .16 mm. 

 thick, while Q. coccinea is about .15 mm. thick and Q. schneckii 

 and Q. macrocarpa are about .13 mm. thick. The thinness of 

 the leaf of Q. schneckii seems to be due to the thinness of the 

 palisade parenchyma, and the thinness of the leaf of Q. mac- 

 rocarpa seems to be due to the thinness of the spongy paren- 

 chyma. The spongy parenchyma, as well as the palisade 

 parenchyma, is more compact in Q. macrocarpa than in the 

 others. (See figs. 13 to 16, inclusive.) 



Midrib. 



In the cross-section of the midrib there are three layers of 

 phloem tissue, a fact characteristic of the oaks (Solereder). 

 There is also xylem tissue with the middle layer of phloem. 

 The xylem is above the phloem in the middle layer, or the 

 phloem is said to face the upper surface of the leaf. In trac- 

 ing this middle layer of xylem and phloem from the base of 

 the leaf to the apex it is found that the xylem disappears, or 

 unites with the upper layer of xylem before the phloem does. 

 The middle layer of phloem always unites with the upper layer 

 of phloem, but in different ways in the different species, and 

 also at different distances from the base of the leaf. 



In Q. rubra this layer of phloem usually extends about half 

 the distance from the base to the apex. At this point the last 

 or uppermost large vein usually branches off from the midrib. 

 The upper layer seems to divide in the middle and the ends 

 bend down. At the same time the middle layer of phloem 



