32 KANSAS UNIVERSITY SCIENCE BULLETIN. 



on the stem, leaf, and involucre scales, also fragments of resin 

 found in the flower. He characterizes the substance as very 

 slightly soluble in water, readily soluble in benzene, alcohol, 

 ether and chloroform, showing an acid reaction when in solu- 

 tion, and combined with the alkalies yielding an amorphous 

 compound, which has the properties of resin soap. 



THE LEAF. 



The structure of the leaf was determined from specimens 

 preserved in chloral hydrate, bleached in potassium hydroxide, 

 and mounted in glycerine, and from material preserved in 

 formalin, imbedded in paraffin; sectioned and stained with a 

 double stain of safranin and Delafield's hematoxylin. 



Anatomically the leaf presents some striking features. It 

 averages 2.3 cm. in length, is rather thick and of a dull gray 

 color, the dullness probably caused by crests and ridges of the 

 cuticle. 



When bleached it has the appearance of a pellucid network, 

 due to the unusual character of the leaf tissues. (Figs. 1 

 and 3.) Water-storage tissue, made up of relatively large 

 parenchyma cells, surrounds masses of other mesophyll cells 

 that contain chloroplasts, but are not differentiated into pali- 

 sade and spongy tissues. (Figs. 3, m and h; 5, u and v; and 6, 

 c and d.) These chlorophyll-bearing cells resemble palisade 

 tissue more than spongy tissue in both form and arrangement. 

 Warming (18) mentions the fact that palisade tissue is greatly 

 developed in xerophytes, either by an increase in the number 

 of layers or in the height of the cells, and also mentions that 

 there is a difference of opinion as to the significance and cause 

 of this structural feature. He regards regulation of transpira- 

 tion as the most essential reason for the structural differences, 

 with light as a very important factor. 



Clements (5) suggests that when the photosynthetic cells are 

 all palisade cells, the condition may have been brought about 

 by low water content. 



The water-storage cells surround each vascular bundle, and 

 extend to the epidermis above and below, thus giving the leaf 

 the appearance of a network of large cells surrounding areas 

 of smaller-celled tissue (fig. 5, v and it) . A remarkable char- 

 acteristic of the leaf is its capacity to hold water, for the water- 

 storage cells occupy about one-third of the volume of the 

 leaf (fig. 2, e). 



