COTYLEDONS AND LEAVES OF CERTAIN PAPILIONACEAE 243 



function for a time as leaves, the anatomical structure is strikingly 

 different in cotyledons and leaves. Every plant examined has ijla- 

 brous cotyledons, while leaves of the same species nearly always bear 

 trichomes. The cotyledons, in all cases, have stomata on both sur- 

 faces, but some of the leaves have stomata only on the lower surface. 

 Frequently there is a difference in the shape of the epidermal cells. 

 Where this occurs the cell outlines are more wavy in the leaves than 

 in the cotyledons. The reverse condition never occurs. The spongy 

 tissue is frequently much more loose in the leaves than in the cotyle- 

 dons. Glandular cells, or cells free from chlorophyll, may occur in 

 the leaves but never in the cotyledons. The stalk of the cotyledon, 

 when present, has a structure different from that of the leaf-stalk. 

 The writer does not wish to generalize from the facts given here, but 

 intends to continue the study in other plant families. 



Explanation of Figures 



1. Psoralen hypogiva ; diagram of cross section of stalk of cotyledon. The two 



vascular bundles are close together. Xylem dotted, stereom black, phloem 

 white. 



2. Psoralea kypocjcea; diagram of cross section of leaf-stalk. The vascular bun- 



dles, five in number, are arranged in a circle with the phloem facing outward. 



3. TrifoUum dasyphyllum ; diagram of cross section of the stalk of the cotyledon. 



4. TrifoHum dasyphyllum; diagram of cross section of leaf-stalk. 



5. Hedysnrum mackenzii; epidermis of lower surface of cotyledonX160. 



6. Heydsarum mackenzii; epidermis of lower surface of foliage leaf X160. The 



wavy outline of the cells gives them an appearance very different from the 

 epidermal cells of the cotyledon. (Fig. 5.) 



7. GlycyrrMza lepidota; vertical section of leaf X160. Tlie large cells in the pali- 



sade region are filled with brownish granular contents. Such cells do not 

 occur in the cotyledons of the same plant. 



8. AsLrar/alus flexnosus; vertical section of leafXl60. The palisade is composed 



of narrow, cylindrical cells and the spongy tissue has many cavities. 



9. Astragalus flexuosus ; vertical section of cotyledonX160. The palisade is com- 



posed of about three layers of cells which are much broader than those in 

 the foliage leaf. The air cavities of the spongy tissue are not large. 



