242 UNIVERSITY OF COLORADO STUDIES 



many plants. The trichomes of the leaves, in the plants examined, 

 are frequently abundant on the lower surface, but few or none are 

 present on the upper surface. Only Petalostemon, cand'ulus and 

 Glycyrrhiza lepidota are without trichomes. 



Internal Structure of Leaf and Cotyledon. The cotyledon 

 (Fig. 9) is generally thicker than the foliage leaf. The palisade is 

 composed of rather broad, cylindrical cells usually forming about 

 three rows. The spongy tissue consists of cells which are spherical 

 or nearly so. No very large air spaces are present. Vascular tissue 

 is poorly developed and there is usually no prominent mid-rib. In 

 the foliage leaf (Fig. 8) the palisade cells are narrower and form 

 about two rows. Air spaces of considerable size are found in the 

 spongy tissue which is made up of cells quite irregular in form. 

 A prominent mid-rib is present and the veins are generally larger 

 than those of the cotyledon. While the structures just described are 

 the rule certain exceptions must be noted. Thus the spongy tissue 

 of the leaf of Amorpha canescens resembles that described above 

 as typical for cotyledons and the spongy tissue of the cotyledons in 

 Rohinia pseudacacia shows a similarity to the structure usually seen 

 in foliage leaves. Cells without chlorophyll occur in the palisade of 

 of the leaves of Psoralea hypogaea but not in the cotyledons of the 

 same species. Large cells with brownish contents are found in the 

 leaves and leaf-stalks of Uedysarum mackenzii and Glycyrrhiza 

 lepidota (Fig. 7), but are entirely absent from the cotyledons. 

 These cells have been examined and described by Bokorny^') for 

 Hedysarum mackenzii. In Glycyrrhiza the secretory cells are 

 of the same kind but occur only in the palisade region, not scattered. 

 In Petalostemon Candidas there are numerous, spherical, multicel- 

 lular glands in the mesophyll and particularly at the margins of the 

 leaf. None are present in the cotyledons. 



SuTninury and Conclusions. It has long been held that there is 

 no general relation in shape between the cotyledons and leaves in the 

 same species of plant. This view is confirmed by the studies here 

 recorded. In the plants examined, all of which have cotyledons which 



(1) Fide Solereder. Compar. Anat. der Dicotyledonen, 296. 1899. 



