14 MISSISSIPPI EXPERIMENT STATION. 



and are about 76m long; in the hybrid, they are about the same as in 

 N. sylvestris. The spongy parenchyma in each of the three plants is 

 made up of loosely connected cells with nimierous large intercellular 

 spaces; N. sylvestris and the hybrid have about the same amount, 

 while N. Tabacum has somewhat more. The epidermal cells vary 

 considerably in size and shape in each plant, but no important differ- 

 ences between the different species were noted. There are epidermal 

 hairs on both sides of the leaves on all three of the plants, and stomates 

 on both sides also, being slightly more on the under side; these were 

 practically the same in the different species. 



The leaf mid-rib was sectioned and studied but the results ob- 

 tained were not very satisfactory. There seems to be considerable 

 difference in the structure of the mid-rib in the two parent species, 

 but since the structure in one species varies considerably with a slight 

 difference in age and position it was not possible to make satisfactory 

 comparisons. However, the mid-ribs of the hybrid showed an inter- 

 mediate structure in so far as could be determined. 



Anthers: As was mentioned above, the anthers of N. Tabacum 

 are considerably thicker than those of N. sylvestris (figs. 14, 15, and 30), 

 but not so long, while the anthers of the hybrid ar« intermediate in 

 both thickness and length. The epidermal cells are papillose in each 

 of the three and similar. The outer wall of the loculus is made up 

 principally of large parenchyma cells with spiral or band-like thick- 

 enings in their walls. In N. sylvestris, for most of the distance along 

 the loculus, there is only one layer of these large cells, and one to two 

 rows of smaller ones; in N. Tabacum there are two or more layers of 

 the larger ribbed cells, and some smaller ones. In the hybrid, these 

 cells are similar to the corresponding cells in the pistillate parent, both 

 in number and size. 



The placenta-like outgrowth extending out into each cell of the 

 anther is really a modification of the wall that formerly separated the 

 loculi. This growth varied considerably in different anthers in the 

 same species, but as a rule, it was larger in anther cells of the hybrid, 

 where there was not much poUen. The poUen grains are spherical in 

 both parent species and 24m in diam. In the hybrid they are nearly 

 all shriveled and defective, merely the collapsed cell wall being present. 



Calyx : Cross sections of the ovaries of each of the plants imder 

 comparison were made, together with sections of the calyx and corolla 

 surrounding. From these sections the ones passing through the thick- 

 est part of the ovary were chosen for comparison. 



In N. sylvestris, the calyx averages about 225m in thickness, in 

 N. Tabacum it is about 255m thick and in the hybrid 225m. Inter- 

 cellular spaces are not so abundant in the calyx of N. sylvestris as in 

 the other two species. 



Corolla: The corolla of N. sylvestris sectioned as mentioned 

 above, showed a thickness of 220m, N. Tabactim corolla 412m, and the 

 hybrid 330m. The corolla of N. Tabacum where sectioned, is made up 

 chiefly of parenchyma cells fitting together closely. A corresponding 

 section of N. sylvestris corolla showed cells very loosely joined, while the 



