278 KANSAS UNIVERSITY SCIENCE BULLETIN. 



close wooliness, which is partly deciduous with age; branches 

 slender, leaves varying from deltoid ovate or almost hastate 

 to rhombic lanceolate, obtusely and finely serrate, sometimes 

 sparingly incised, on slender petioles, with sterile heads rather 

 loosely racemed, spines of the ovoid two-flowered involucre 

 flat and thin, broadly lanceolate, subulate, pubescent, or 

 almost glabrous." 



In harmony with its environment, this plant has protective 

 devices, limiting transpiration. The leaves are comparatively 

 small, varying, in specimens studied, from 9 mm. to 29 mm. 

 in length, and from 2 mm. to 16 mm. in width. They are seen 

 to be hoary, with a gray pubescence, this thick covering of 

 hairs minimizing the loss of water caused by its desert en- 

 vironment. Compensating the smallness of the leaves, the 

 stem subepidermal tissues contain chloroplasts. 



The leaves are borne by slender petioles on so much short- 

 ened branchlets that they seem many times almost to originate 

 in one plane. These shortened branchlets are of approxi- 

 mately equal length, and are arranged alternately by thirds 

 upon the older branches. 



Gsertneria deltoidea is a low winter perennial, showing in 

 all its phases a pronounced xero phytic structure. As just in- 

 dicated, its greatest development occurs during the winter 

 months, when it blooms and produces its fruits, which are 

 bur-like, and are armed with several ranks of prickles or 

 spines. These reach maturity and are ready to be dispersed 

 by animals or other carriers early in April. The low diflFuse 

 habit of the plant, as a whole, is adapted to two main facts : 

 first, the drying effect of high winds ; and second, the intense 

 heat and light of the desert environment. 



In this study the drawings were made, for the most part, 

 by means of the camera lucida and the projection lantern from 

 sections and macerations of formalin material. 

 HISTOLOGY OF THE LEAF. 



In presenting the histology of this part of the plant, the 

 discussion of its cellular anatomy naturally falls under three 

 general heads : first, the epidermal tissues ; second, the funda- 

 mental tissues ; and third, the vascular system. 



The Epidermis. 

 The epidermal cells are variable in size. The inner tangen- 

 tial and radial walls are cellulose, the outer wall is cellulose 



