io8 BOTANICAL GAZETTE [febrtjary 



narrow, and of a decidedly xerophytic form and structure as com- 

 pared with rosette leaves. 



5. The outer epidermal wall of rosette leaves is thicker , as a 

 rule, than in stem leaves. The maximum thickness occurs in 

 middle stem and apical rosette leaves. The thickness of the 

 cuticle varies with the thickness of the epidermal wall, the thickest 

 walls having the thickest cuticle. Rosette leaves in the large 

 majority of instances have the thickest cuticle. The preponder- 

 ance of epidermal protection is in favor of rosette leaves. In stem 

 leaves of xerophytic form the preponderance of epidermal protec- 

 tion is in favor of stem leaves. 



6. In a comparison of the different stem and rosette leaves of 

 the same plant it is obvious that the lowest stem and lowest rosette 

 leaves, as well as the basal part of all leaves, have the thinnest 

 epidermal wall, thinnest cuticle, the most poorly developed palisade 

 tissue, the maximum development of spongy tissue and air spaces, 

 and the minimum development of chloroplasts. The upper stem 

 leaves are relatively xerophytic in structure, especially in the 

 apical region of these leaves. The middle and lower stem leaves 

 are usually thinner than the corresponding rosette leaves. The 

 palisade parenchyma in stem leaves usually is better organized, 

 more compact, and the cells relatively longer and narrower, as 

 compared with the thickness of the leaf, than in rosette leaves. 

 The thickness of palisade cells of rosette leaves is greater, in most 

 cases, than in stem leaves. This is also true of the absolute length 

 in the great majority of instances. 



7. When the chlorenchyma in middle stem and middle rosette 

 leaves is compared we may conclude: (1) that rosette leaves, in 

 most cases, have a greater amount of chlorenchyma than stem 

 leaves (this is especially true of spongy parenchyma) ; (2) that in 

 most cases rosette leaves also have more air spaces than stem 



1 



leaves; (3) that there is little difference in the number of palisade 

 layers in the two kinds of leaves, but in most cases the absolute 

 size of the palisade cells (length and thickness) is greater in rosette 

 than in stem leaves ; (4) that the average size of cells of the spongy 

 parenchyma is also greater in rosette than in stem leaves; (5) that 

 sclerenchyma tissue is about equally developed in both kinds of 



