12 .MISSISSIPPI EXPERIMENT STATION. 



and size of the calyx is intermediate between the same of the two parents, 

 as is also the length of the stamens and shape and size of the anthers. 

 The seed pods, in so far as they develop, seem to be intermediate m 

 size and form. They become shriveled and contain but few seeds. 

 The majority of the flowers set no seed at all ; this is due to the lack of 

 pollen, only a small quantity being produced, and this consists nearly 

 altogether of defective, shriveled grains. 



This cross was repeated in 1909 and the hybrids produced were, 

 apparently, similar to the ones described. 



Nicotian 1 Tabacum, N. sylvcstris and Hybrid. 



HISTOLOGICAL STRUCTURE. 



Stems. (Cross section of stem of each 30 cm. above ground). 



The cortex is comparatively thick in each of the three plants; in 

 N. Tabacum the entire thickness (extending from the outside to cam- 

 bium), is 1055m; in N. sylvestris it is 945m thick and in the hybrid 1350m. 

 The main portion of the cortex consists, in each case, of thin walled 

 parenchyma cells rather loosely united. The number of large thin 

 walled parenchyma cells is somewhat greater in N. Tabacum, and in 

 the hybrid than in N. sylvestris; these cells average somewhat larger 

 in the hybrid than in N, Tabacum (figs 9, 10 and 11). The number of 

 layers of cortical cells is aboitt the same in the three plants. The 

 nuclei of these cells are about the same size in N. Tabacum and N. 

 sylvestris, — being about 15 - 17m in diam., while in the hybrid cells 

 they seemed to vary in size, ranging from 12 - 24m in diam. 



In the inner part of the cortex of each, are strands of bast fibers. 

 In N. sylvestris, these fibers are in clusters of 4 to 20, and the clusters 

 are so numerous that they form a nearly continuous band arovmd the 

 stem. The average diameter of each fiber is 54m, the cell wall being 

 about 4m thick on the average. In N. Tabacum, these clusters are 

 more scattered and only 2 to 10 in a cluster; the average width of each 

 fiber is 42m, while the average thickness of the cell wall is about 10m. 

 In some fibers the lumen is practically absent, while in the fibers of 

 the N. sylvestris there is a comparatively large lumen in each fiber. 

 In the hybrid, there are scattered clusters about the same as in N. 

 Tabacum; average width of each fiber is 60m, wall thickness 9m. These 

 fibers are slightly larger than the fibers of the staminate parent, N. 

 sylvestris, while they have a wall thickness about the same as the 

 fibers in the pistillate parent. However, in the hybrid they vary in 

 size considerably more than in either parent. 



Phloem : In each of the three plants the phloem strands are small 

 and not very distinct from the neighboring cells of the inner part of 

 the cortex. However, rather large sieve tubes and small companion 

 cells can be identified. In N. Tabacum, the sieve tubes are from 

 18 - 24m in diameter, and in N. sylvestris 15 -21m. In the hybrid 

 they are about the same size as in N. Tabacum. 



Xylem: The xylem or wood of the stem is well developed in 

 each of the three plants. In N. sylvestris, it is about 1600m thick, in 



