98 BOTANICAL GAZETTE . [February 



for substances passing from cell to cell. No chloroplasts are 

 present in epidermal cells except in guard cells, and, to a slight 

 extent, in winter leaves of Leonurus Cardiaca. 



As to size, the upper epidermal cells are larger than the lower, 

 and, with few exceptions, the epidermal cells of rosette leaves are 

 larger than those of stem leaves. In 80 per cent of all observations 

 made the epidermal cells of rosette leaves were found to be larger 

 than those of stem leaves. The size of epidermal cells is somewhat 

 correlated with the size of leaves, the larger leaves haying the 

 larger epidermal cells; but there are so many exceptions to this 

 that such a general statement is not warranted. 



The vertical diameter of epidermal cells is greater, as a rule, 

 in rosette than in stem leaves (true of 80 per cent of cases), in the 

 upper than in the lower epidermis, and usually increases from 

 the apex toward the base of the leaf. In the middle rosette leaves 

 the maximum diameter is usually found in the middle of the leaf. 

 In Capsella there is a gradual increase from the upper stem to the 

 lowest rosette leaves. As a rule, the maximum diameter is attained 

 in both the middle stem and rosette leaves. 



Blade, epidermal wall, and cuticle 



The blade decreases in thickness from the apex to the base 

 of the leaf. It also decreases from the upper to the basal leaves. 

 This is less apparent in middle leaves, where the leaf sometimes 

 increases in thickness from apex to base, or where the maximum 

 thickness of the blade occurs in the middle of the leaf. Those 



most 



Rosette 



yes are thicker than stem leaves, owing to a greater development 

 spongy parenchyma. This is true more particularly of the 



middle and basal stem 



stem 



especially the apical portions of those leaves, are frequently thicker 

 than the corresponding portions of rosette leaves. The blade, in 

 most instances, also appears thicker than the blades of stem leaves. 

 Notable exceptions are Arabis lyrata, A. laevigata, Linaria cana- 

 densis, Leonurus Cardiaca, Campanula rotundifolia, and Monarda . 

 punctata. All these species, except Leonurus Cardiaca, have either 

 linear or oblong lanceolate stem leaves, while the basal leaves 



