196 KANSAS UNIVERSITY SCIENCE BULLETIN. 



food in the stem. The phloem portion is very little differen- 

 tiated; it consists only of cambiform cells and undivided 

 mother cells of the sieve tubes, there being found neither sieve 

 tubes nor sieve parenchyma cells. 



6. Storage Tissues. — Since Toivnsendia grows in a xero- 

 phytic habitat it is not surprising to find in it some provision 

 for the storage of water. In the stem, the cortex, medullary 

 ray and pith cells are well adapted to the storing of water. 

 In the leaf, however, special provision is made: throughout 

 the whole length of the leaf are found large water-storage 

 cells which not only reduce transpiration but also rapidly fill 

 whenever the water supply is increased, and yield their con- 

 tents to the assimilating cells as the supply of water there is 

 reduced. 



7. Aerating Spaces. — As would be expected to be found in 

 a xerophyte, the amount of space devoted to aeration is com- 

 paratively small. Only one one hundred and tw^enty-fifth of 

 the volume of the leaf of Toivnsendia is devoted to aeration ; 

 While in Pistia about two-thirds of the volume of the leaf is 

 thus employed. 



LESQUERELLA SPATULATA. 



Lesquerella spatulata is perennial by a much branched 

 caudex which varies from one to two inches in length. It has 

 a taproot which measures from one foot to a foot and a half in 

 length and one-fifth of an inch in diameter at its thickest por- 

 tion. The leaves are separated by short internodes and ap- 

 pear tufted. They measure from one-half to one inch in 

 length and one-fifth to one-seventh of an inch in width. They 

 are entire and vary in form from narrowly elliptic to ovate- 

 lanceolate, oblanceolate and spatulate, and they, as well as the 

 pedicels, are beset with stellate hairs. The flowers are yellow 

 and are borne on pubescent scapes which measure from one- 

 half inch to six inches in length. 



The Stem. 



The Tegumentary Tissues. — The protection of the mature 

 stem is provided for by a cutinized epidermis and cork. There 

 is, in addition to these tissues, in older portions of the stem, a 

 borke. All of the walls of the epidermis are cutinized. Figure 

 37 represents a small portion of the epidermis as seen in cross 



