MISSISSIPPI EXPERIMENT STATIOX. 2:i 



of large cells with thickened bars in their walls; N. alata has but one 

 layer of those large cells around a considerable part of its wall, but there 

 are about two layers of small cuboidal cells within this layer; N. Tabacum 

 does not have these cuboidal cells clearly defined. The loculus wall of 

 the anthers of the hybrid is rather intermediate ; although there are not 

 quite so many cells, it has rows of large, ribbed cells similar to X. Taba- 

 cum, while the small cuboidal cells on the inside are rather prominent. 

 Pollen grains in N. Tabacum are 24/x in diameter, and nearly spheri- 

 cal; in N. alata they are about 30m in diameter, and are slightly angular, 

 many appearing obtusely triangular in section; the pollen grains of the 

 hybrid are nearly all small, shriveled, and defective. The few that 

 were nearly perfect were about spherical and had a diameter of 27 - 30/j . 



Ovaries: Excepting some difference in size, the ovaries of the 

 three plants are similar in structiire and general arrangement of parts. 



Corolla: (Cross sections of the part of the corolla tube sur- 

 rounding the ovary were used.) The sections of N. Tabacum are 412/i 

 in thickness. The epidermal cells on either side of these sections are 

 palisade in form, 39m long and 13m wide; the cells in the central part of 

 the section are spherical and fit together closely. The calyx of N. 

 Tabacum is 225m thick (fig. 21). N. alata has a corolla 270m thick, the 

 epidermal cells being decidedly paHsade in form and arrangement, and 

 are about 57m long and 24m wide; the mesophyll cells are loosely joined. 

 The calyx is 217m thick. It has a layer of peculiar thick-walled lignified 

 ceUs just beneath the inner epidermal cells. These cells are about 15m 

 long and vary considerably in width, the majority being about 6m wide 

 (fig. 17). 



In N. Tabacum x N. alata, the corolla is 210m thick, epidermal cells 

 palisade, 45m long on the outside of corolla and 33m long on the inside. 

 The mesophyll cells are rather closely joined. The structure of the 

 coroUa is very similar to that of N. Tabacum, but in thickness it is more 

 like N. alata. The calyx is 250m thick, and has a layer of sub-epidermal 

 thick- walled cells of the same character, size and shape as in N. alata 

 (fig. 19). 



