102 BOTANICAL GAZETTE [February 



spongy parenchyma are decidedly more irregular in rosette leaves, 

 and the tissue contains a maximum of air spaces. Palisade tis- 

 sue is least developed in basal stem and rosette leaves, as well as 

 in the basal region of the leaves themselves. 



Chrysanthemum Leucanthemum. — The outer epidermal wall 

 and cuticle of the upper and middle stem leaves are very much 

 alike in thickness, but both are decidedly thicker than the corre- 

 sponding epidermal wall and cuticle of the basal stem leaves, 

 the latter being only about one-half as thick. Rosette leaves do 

 not differ much from each other in the thickness of epidermal 

 wall and cuticle, but the maximum thickness may probably be 

 found in the middle leaf. Rosette leaves, as a whole, have a 

 thinner epidermal wall and cuticle than stem leaves, being only 

 one-half to two-thirds as thick. The palisade tissue is better 

 developed, as a whole, in stem than in rosette leaves, and decidedly 

 better developed in both stem and rosette leaves in apical and 

 middle leaves than in basal leaves. The spongy parenchyma is 

 slightly better developed in rosette leaves and in both kinds of 

 basal leaves. Here is found also the maximum development of air 

 spaces. 



Oenothera biennis. — The stem leaves are thickest in the apical 

 region and gradually become thinner toward the base. There is 

 also a gradual increase in thickness from the apical to the basal 

 stem leaves. The upper rosette leaves are thickest in the apical 

 region and become thin toward the base of the leaf. In the middle 

 and lower rosette leaves the greatest thickness is found in the 

 middle region. From this region they gradually become thinner 

 toward both the apex and base of the leaf. 



The spongy parenchyma in stem leaves gradually diminishes 

 from the apical to the basal region of the leaf, but there is a gradual 

 increase in amount from the apical to the basal leaves. In the 

 upper rosette leaves the spongy parenchyma also gradually de- 

 creases from the apex of the leaf to the base. In the middle and 

 lower rosette leaves, however, the greatest percentage of spongy 

 tissue is found in the apical and basal regions. In stem leaves the 

 palisade tissue is most developed in the apical region and least in 

 the basal region. The maximum development is probably found 



