262 UNIVERSITY OF COLORADO STUDIES 



in size after coming above ground and function as leaves for a long 

 time. Although thicker than the leaves they may be described as 

 foliaceous. 



Epidermis as seen in surface view. — The epidermis is composed of 

 cells with a very wavy outline. On the whole, they are about alike 

 in cotyledon and leaf. Stomata are, however, absent from the upper 

 face of the leaf. A row of multicellular hairs occurs along the margin 

 of the leaf. No such hairs were seen on the cotyledon. 



Internal structure. — The palisade cells of the leaf are narrow and 

 placed close together. In the spongy parenchyma there are about 

 four rows of cells. The cotyledon has a loose palisade with many 

 large intercellular spaces. All the cells of the cotyledon are large. 



Cotyledon stalk and leaf petiole. — Neither the cotyledon or leaf has 

 a well-defined stalk, but the basal part of the foliage leaf might well be 

 called a winged petiole. So also, the cotyledon is very much narrowed 

 at the base. Sections were made of these narrowed bases. Two well- 

 developed median vascular bundles were found in the cotyledon and, 

 in addition, a small bundle on each side at the margin. In the leaf 

 base there is a single median bundle and two lateral ones not far away. 



Summary 



The foregoing account refers to seedlings of eight different species 

 of tropical plants, for the most part trees and shrubs. It may be con- 

 sidered as a report of progress. Very little is known concerning coty- 

 ledon structure and it was thought that a fully illustrated account of a 

 few species would be of interest. The species were selected because 

 of their foliaceous cotyledons; and both cotyledons and foliage leaves 

 were studied. If the cotyledon be a leaf, as has been generally supposed, 

 we should expect its anatomy to agree with that of the leaf except where 

 modified for storage purposes. A comparative study should throw 

 some light on the nature of the cotyledon. The observed differences 

 in structure of cotyledon and leaf, as shown in the present and in former 

 papers 1 by the author, tend to confirm the view that these two members 

 of the plant body are not really of the same nature. 



1 Published in the Botanical Gazette and in the University of Colorado Studies. 



