MACROSCOPIC AND MICROSCOPIC CHARACTERS OF PLANTS. 



807 



Sections of lower epidermis were taken from the same 

 regions, the cells are slightly smaller than those of the 

 upper epidermis, the sunken cells are similar in appear- 

 ance, and there are numerous stomata. The lower epider- 

 mal cells of D. nobile are larger than those of D. find- 

 layanum, while those of the hybrid are, as a rule, smaller 

 than those of either parent, except at the base of the 

 lamina where the cells are in length between those of 

 the parents. The average size for the entire lamina is 

 much narrower than either parent and very slightly 

 longer than in D. findlayanum. (Table J 35.) 



The sunken epidermal cells are more numerous in the 

 hybrid than in either parent, in which respect it is nearer 

 D. nobile in which they are more numerous than D, 

 findlayanum. (Table J 5.) 



The stomata are also more numerous in the hybrid 

 than in either parent, except at the base of the lamina 

 where they are less numerous. The average number in a 

 field for the entire lamina is greater in D. findlayanum 

 than in D. nobile, while in the hybrid it is greater than in 

 D. findlayanum. (Table J 35.) 



TABLE J 35. The number of stomata in a field on the lower 

 epidermis. 



Transverse sections of the lamina (Plate 32, figs. 193, 

 194, and 195) were made at a point midway between the 

 apex and base, and examined at the midrib. The upper 

 epidermal cells directly above the center of the midrib are 

 only slightly elongated, but toward the sides they are 

 greatly elongated, forming a ridge on each side of the 

 midrib. These ridges are larger in D. nobile than in 

 D. findlayanum, but are not nearly so pronounced in the 

 hybrid as they are in the parents. The cells have on the 

 inner and lateral faces rather thick walls, while the outer 

 face has a thick cuticle. The cells directly above the 

 center of the midrib are deeper in D. findlayanum than in 

 D. nobile, while those of the hybrid are in depth of a 

 mid-degree of intermediateness between the cells of the 

 parents. The cells forming the ridges are more elon- 

 gated in D. nobile than in D. findlayanum, while those 

 of the hybrid are not elongated nearly as much as in 

 either parent. (The statistics are given in Table J 36.) 



The lower epidermis is a layer of smaller almost 

 square cells with thickened inner and lateral walls and a 



TABLE J 36. 



thick cuticle on the outer wall. These cells are of the 

 same depth in D. findlayanum and D. nobile, but not 

 quite as deep in the hybrid as in the parents. 



Between the two epidermal layers is the midrib 

 bundle, separated on each side from the epidermis by 

 two layers of mesophyll tissue. It consists of a lower- 

 most, somewhat crescent-shaped area of heavily thickened 

 cells, the sclerenchyma. Directly above this is a small 

 patch of thin-walled cells, phloem cells, and sieve tubes. 

 Uppermost is a large area of large, open, heavily thick- 

 ened cells, the xylem, in the middle of which there is a 

 small patch of protoxylem. The midrib bundle is deeper 

 in D. findlayanum than in D. nobile, but wider in D. 

 nobile than in D. findlayanum. In the hybrid it is much 

 smaller in both dimensions than in either parent. (Table 



J37 ') TABLE J 37. 



Transverse sections of the leaf examined at the re- 

 gion of a bundle midway between the midrib and the 

 margin show the upper epidermis to be a layer of large 

 rectangular cells with lateral and inner walls only slightly 

 thickened, and with a thick cuticle on the outer face. 

 The upper epidermal cells are larger in D. findlayanum 

 than in D. nobile, and in the hybrid are in size between 

 those of the two parents, but in depth nearer that of 

 D. nobile and in width nearer that of D. findlayanum. 

 The cuticle on the outer wall is much thicker in D. nobile 

 than in D. findlayanum, while in the hybrid it is not 

 as thick as in the parents. (Table J 38.) 



TABLE J 38. 



'Upper. 'Lower. 



