iyiy] STOBER— WINTER AND SUMMER LEAVES 103 



in the apical and middle regions of the basal leaves. The palisade 

 cells of rosette leaves are decidedly broader or thicker than those 

 in stem leaves, but are relatively slightly longer. The maximum 

 development is found in the apical and middle regions of the leaf, 

 or in those parts of the leaves having the greatest exposure to light 

 and other desiccating influences. 



The largest epidermal cells are found in the middle region of both 

 stem and rosette leaves. It is also in the middle of leaves that 

 both upper and lower epidermal cells have the greatest vertical 

 diameter. The outer epidermal wall and cuticle of stem leaves 

 are thickest in the apical leaves, and gradually become thinner 

 toward the basal leaves. In the upper stem leaves the outer 

 wall and cuticle diminish from the apical to the basal region. In 

 the middle and basal stem leaves there is less difference, and in the 

 lowest leaves there is practically no difference in thickness of the 

 epidermal wall and cuticle in different regions. In the upper stem 

 leaves there is not much difference in the thickness of the epidermal 

 wall and cuticle of the upper and lower sides of the leaf; but in the 

 lower stem leaves the thickness is decidedly greater in the upper 

 than in the lower epidermis. The greatest difference in thickness 

 is found in the lowest leaves. 



In rosette leaves the situation in thickness of epidermal wall 

 and cuticle is similar to that found in stem leaves. In the upper 

 rosette leaves, however, there is a greater difference in thickness 

 of wall and cuticle between the apical and basal regions of the leaf. 

 The hairs on both stem and rosette leaves are longest and most 

 abundant on the midrib and have larger veins than elsewhere. The 

 hairs are most abundant on the upper stem leaves and gradually 

 diminish in number and size to the basal leaves, where they are 

 quite small (except on veins) and only half or even less than half, 

 as abundant. On the upper leaves they are longer and more 

 abundant on the lower than on the upper surface, and increase in 

 length and abundance from the apex to the base. On the middle 

 stem leaves they are similar in size and abundance on both sides 

 of the leaf, but slightly decrease in number from apex to base. 

 On the basal leaves the hairs are considerably reduced in size, but 

 otherwise the situation is similar to that found in middle stem 



