22 MISSISSIPPI EXPERIMENT STATION. 



In N. alata, the first layers of hypodermal cells are decidedly different 

 from underlying cortical cells. They are well supplied with chloro- 

 plastids and simulate the mesophyll of leaves in appearance, the first 

 layer being made up of cells more or less cylindrical, and arranged in 

 palisade fashion, while the cells just under these are shorter and loosely 

 joined. They may be compared to the spongy parenchyma of leaves. 

 (Fig. 12.) The corresponding cells in the hybrid are intermediate; the 

 first layer has rather large cells, and they are somewhat palisade in 

 form and arrangement, but they fit together closely. The next layers 

 under this are similar to cortical cells, and have no large intercellular 

 spaces. The bast fibers in N. Tabacum average 42m in diameter and 

 the cell wall is 10m thick; in N. alata the fibers average about 55m in 

 diamater with a wall thickness of 3m ; in the hybrid the fibers are of two 

 sorts, some about 60m in diameter with a wall 3m thick, others being 

 about 28m in diameter, and having a wall 4.5m thick. The larger ones 

 resemble N. alata bast fibers, rather closely, while the small ones are 

 much like bast fibers found in the other parent. 



The xylem vessels of N. Tabacum are 65m in diameter, in N. alata 

 they are 45m, and in the hybrid, about 35m; tracheid cells are respect- 

 ively 20, 18, and 22m in diameter. 



The medullary rays, in the sections of N. alata and hybrid exam- 

 ined, were not clearly differentiated, while in N. Tabacum they were. 

 In this species the ray cells have thin, cellulose walls in marked contrast 

 to the lignified tracheids and xylem vessels (figs 9, 12 and 13). 



The pith cells are large, thin-walled, sub-spherical cells in each of 

 the three plants; in N. Tabacimi they are 150 - 230m in diameter; in 

 N. alata 120 - 222m, and in the hybrid 100 - 150m. The nuclei of the 

 pith cells are very prominent ; they vary in size considerably in a single 

 species, but are considerably larger on the average in N. Tabacum than 

 in the other plants compared; in N. Tabacum they are from 12 - 30m 

 in diameter, 9 - 21m in N. alata, and 7 - 12m in the hybrid. 



In the periphery of the pith of the stem, are a few fibers in each; 

 these are similar to the bast fibers found in the same species. They are 

 scarce in N. alata and rather plentiful in N. Tabacum and the hybrid. 



Leaves : The leaves of the three plants have about the same thick- 

 ness and are very similar in structiu-e. They all have stomates on 

 both sides, being more numerous on the under side in each case. All 

 three have hairs on both sides of the leaves; these are about the same 

 in size and quantity. 



Anthers: The anthers of both parents are considerably larger 

 than those of the hybrid; in N. Tabacum they are 2220m ^\'ide (widest 

 part), 2850m in N. alata and 2025m in the hybrid. The anthers of the 

 two parents differ considerably in shape, the anthers of N. Tabacum 

 appearing in cross-section somewhat like a butterfly with wings spread 

 (figs. 30, 31, and 32), whUe the cross sections of N. alata anthers look 

 like cross-sections of two parallel cylinders that are slightly connected 

 laterally. 



The wall surrounding the anther loculi is different in the two parent 

 species. In N. Tabacum, it has in its central part, two or more layers 



