8o 



BOTANICAL GAZETTE. 



[ March, 



" strengthening cells," or to the division of the epidermal 

 cell of the outer leaf surface into three layers. This arrange- 

 ment serves, of course, to give still further rigidity to the 

 leaf apex. At this part of the leaf the epidermal cells of the 

 inner surface are much longer than those of the outer surface 

 (as 



seen in this section); seeming 



in the one case to be 



10, cf. also 



Fig. 8. Section of stoma of Pinus 



sylvestris x 650. 



lengthened, in the other shortened (figs. 9 and 



fig- 3). 



The stomata in surface slice appear widely elliptical and 



have the depressed position usually found in thick-skinned 



parts. In size, they are perhaps 

 from one-third to one-half that of 

 the surrounding epidermal cells, 



4 M A ^B m 



and are relatively equal to each 

 other. The stomata are irregu- 

 larly arranged in this view, both 

 is regards the surrounding epi- 

 dermal cells and the relation of 

 their axes. In transverse section 

 the guard cells are almost per- 

 fectly oval, with their outer walls 

 heavily thickened or from three 

 to five times thicker than their inner walls. This thickening 

 appears to be greatest at or near the point of union with the 

 subsidiary cells, but extends in an almost undiminished de- 

 gree to the free ends. The free ends show no difference 

 either in shape or size from the united ends, presenting a 

 marked contrast to Pinus, in which the reverse is true. They 

 meet each other at an angle of about 45 as referred to their 

 longer diameter, and open into a remarkably large respira- 

 tory cavity. (Fig. 7.) j © 1 



The adjoining epidermal cells are but slightly modified, 

 those immediately adjacent having their lateral walls which 

 join the guard cells modified in shape onlv as would be indi- 

 cated by the outline of the guard cells. The inner walls of 

 these cells are in most cases more irregular in outline and 

 more heavily thickened than the ordinary epidermal cell. 



the guard cells are depressed below the surface about 

 one-half the height of the epidermal cells, so that in a surface 

 slice it is necessary to focus down to bring them in view. 

 1 he epidermal cells next removed from the subsidiary cells 

 are somewhat shortened, becoming almost isodiametric as 

 viewed in both transverse and surface sections. The subsid- 

 iary cells are also as a rule more heavily thickened and cu- 



