286 KANSAS UNIVERSITY SCIENCE BULLETIN. 



The xylem is made up of tracheal tubes, tracheids, wood 

 fibers, and sclerotic wood parenchyma cells. (See figs. 49, 50, 

 and 51.) Tfie tracheal elements consist largely of tracheal 

 tubes having many small bordered pits, and occasional ridges 

 in the walls. Here, as in the stem xylem, were noted at more 

 or less regular intervals the thickened rings in the tubes. (See 

 fig. 51.) The other xylem tissues and those of the phloem do 

 not diff'er essentially from those of the stem, so they will not 

 need to be discussed further here. The root hairs are numer- 

 ous, and as stated above, are remarkable for the tenacity of 

 their hold, even after the transformation of the cortical tissue 

 into cork has cut them off from nourishment and caused them 

 to die. They are found, after this condition has come about, 

 to be suberized on the outer portion of their walls with a cellu- 

 lose inner layer. 



RESUME. 

 The plant, as a whole, is xerophytic. Its characters may be 

 summarized as follows : 

 Protective Devices: 



Low habit of growth. 



Small leaves. 



Heavy hairy covering. 



Heavy cutinization of all exposed surfaces. 



Secreting glands and spaces. 

 Strengthening Tissues: 



Anastomosing bast ring. 



High lignification. 



Complete silicification. 



Heavy secondary thickening of pith region. 

 Water Provisions: 



Thick walled and plain pitted storage cells in leaf. 



Restricted evaporating surface. 



Extensive tracheal storage system. 



BIBLIOGARPHY. 



Bentham et Hooker, 1862. Genera Plantarum, vol. 1 ; pt. 1. 



Bergen, J. Y. Transpiration of Spartium jmiceum and other Xerophytic 



Shrubs. Bot. Gazette, vol. 36, p. 464. 

 Blumer, J. C, 1909. An Arizona Mesa. Plant World, vol. 12, No. 1, Jan. 

 Bower, 1908. The Origin of a Land Flora, pp. 9, 480 to 494. 

 Bray, W. L. Ecological Relations of the Vegetation of Western Texas, 



pp. 99-195-262. 

 Britton and Brown. Flora of the Northern United States and Canada. 

 Cannon, W. A., 1905. Water Conducting Systems of Some Desert Plants. 



Bot. Gaz., 39, pp. 396-408. 



