800 



MACROSCOPIC AND MICROSCOPIC CHARACTERS OF PLANTS. 



specks, becoming whitish and greenish white toward the 

 top; in C. eburneum, yellow at the base, then ivory- 

 white spotted with pale purple; in the hybrid yellow 

 at the base, then ivory-white with reddish-brown specks. 

 On the outer surface the color in C. lowianum is yellow- 

 ish white becoming yellowish green at top ; in C. ebur- 

 neum, ivory-white; and in the hybrid, ivory-white, be- 

 coming yellowish green at top. 



COMPARISONS OF MICROSCOPIC CHARACTERS. 

 ROOTS. 



Transverse sections of the roots of C. lowianum, C. 

 eburneum, and 0. eburneo-lowianum made at 1 inch from 

 the tip were examined (Plate 31, figs. 184, 185, and 186). 

 Outermost is the velamen, a zone of water-storing tissue 

 developed from the epidermis, and composed of elon- 

 gated, hexagonal cells with a spiral thread around their 

 walls. This zone varies in width in each plant according 

 to whether or not it is pressed against another surface. 

 The velamen is much wider in 0. eburneum than in 

 C. lowianum, and between the parents in the hybrid, but 

 nearer to C. lowianum than C. eburneum. (Table J 21.) 



The epidermis, the innermost layer of the velamen, is 

 composed of rather large cells which in C. lowianum 

 are very little wider than deep, in fact almost square; 

 in C. eburneum and in the hybrid they are much deeper 

 than wide. They are larger, however, in the hybrid than 

 in either parent. (Table J 21.) 



Immediately interior to the epidermis is a cylinder of 

 cortex, composed of large, open, thin-walled cells. The 

 cortex is much wider in C. eburneum than C. lowianum, 

 and practically mid-intermediate in width in the hybrid. 

 (Table J 21.) 



A great number of isolated sclerosed cells are present 

 in the cortex of C. eburneum. These are entirely absent 

 in C. lowianum and present in the hybrid, though not in 

 such great number. In C. eburneum there are, on the 

 average, 2 of these in a microscopic field ; in the hybrid, 

 1.5. The walls are slightly thicker in C. eburneum than 

 in the hybrid. (Table J 21.) 



The endodermis, the innermost layer of the cortex, 

 is a ring of oval cells, which in the hybrid are exactly 

 mid-intermediate in depth between those of the parents; 

 but are in width identical with those of C. loivianum. 

 (Table J 21.) 



TABLE J 22. 



The central vascular cylinder is composed of a cen- 

 tral zone of pith from which radiate xylem arms, be- 

 tween which are patches of phloem. There are more 

 phloem patches, and consequently more xylem arms, in 

 C. eburneum than in C. lowianum, and less in the hybrid 

 than in either parent. 



The number of phloem patches in C. lowianum is 

 16, in C. eburneum 18, in C. eburneo-lowianum 11. 



The largest vasa are larger in C. lowianum than in 

 C. eburneum, and though between the parents in size in 

 the hybrid they are nearer C. eburneum than C. lowianum. 



The diameter of the largest vasa in C. lowianum is 

 86.4/i, in C. eburneum 57.6/t, in 0. eburneo-lowianum 

 68.4/i. 



LEAF, 



Sections of upper epidermis were taken from the 

 apex, middle, and base of leaves of the same age. The 

 cells are almost rectangular with thick walls, and each 

 contains one rod-shaped crystal. At the apex and base 

 of the leaf the epidermal cells of the hybrid are larger 

 than those of either parent, but at the middle they are 

 exactly mid-intermediate in length, though the same as 

 C. lowianum in width. (Table J 23.) 



The average length of the upper epidermal cells for 

 the entire leaf is greater in the hybrid than in either 

 parent, while the average width is exactly mid-interme- 

 diate between those of the parents. 



Sections of the lower epidermis were taken from the 

 apex, middle, and base of the leaf. The cells are rec- 

 tangular and have thick walls like the upper epidermal 

 cells. At the apex and base of the leaf the cells of the 

 hybrid are in size between those of the two parents ; but 

 at the middle those of the hybrid are longer than those of 

 either parent, and of the same width as in C. lowianum. 

 (Table J 23.) 



TABLE J 23. Lengths and widths of upper and lower epidermis of 



leaves. 



The average size of the lower epidermal cells for the 

 entire leaf in the hybrid is between those of the parents ; 

 the length, however, is nearer that of C. eburneum, in 

 fact almost identical with it, while the width is identical 

 with that of C. lowianum. 



Stomata are numerous on the lower epidermis. At 

 the apex and the base of the leaf the number in the hybrid 

 tends to intermediateness but nearer to C. eburneum. 

 At the middle, however, there is a less number in the 

 hybrid than in either parent. On an average for the 

 entire leaf the number in the hybrid is equal to that of 

 C. eburneum and somewhat less than in C. lowianum. 



