BUNTON: TOWNSENDIA EXSCAPA. 189 



found to be 3.801 sq. mm. Of the xylem portion, 62 per cent 

 was devoted to the conduction of water. In Verbena, then, 

 there was found devoted to the conduction of water seven times 

 as much of the stem as in Toivnsendia. In Mentzelia oligo- 

 s^perma there was devoted to the conduction of water 9 per 

 cent of the stem cross section, where the area was 9.07 sq. mm. 

 Of the xylem portion, 33 per cent was devoted to the conduc- 

 tion af water. In Mentzelia also there was found to be de- 

 voted to the conduction of water nearly seven times as much of 

 the stem as in Townsendia. In Ambrosia artemisifolia there 

 was found devoted to the conduction of water 21 per cent 

 of the stem cross section, where the area was 13.86 sq. mm. 

 Of the xylem portion 52 per cent was devoted to the conduction 

 of water. In Ambrosia, then, there was devoted to the conduc- 

 tion of water about sixteen times as much of the stem as 

 in Toivnsendia. In Abutilon avicennse there was devoted to the 

 conduction of water 2 per cent of the stem cross section, where 

 the area was 38.48 sq. mm. Of the xylem portion, 6 per cent 

 was devoted to the conduction of water. In Abutilon, accord- 

 ingly, there was devoted to the conduction of water approxi- 

 mately twice as much of the stem as in Townsendia. 



When compared with the water-conducting tissues of desert 

 plants, which have have been discussed by W. A. Cannon^ in 

 his paper on the "Water-conducting Systems of Desert Plants," 

 Toiimsendia has a relatively large water-conducting area. 



In the following table is given the number of tracheal ele- 

 ments in 1 sq. mm. of stem, cross section, of Townsendia, and 

 of several mesophytes and xerophytes; the latter cited from 

 Cannon : 



Townsendia , 66 



Mesophytes : 



Abutilon avicennse 33 



Verbena stricta 734 



Mentzelia oligosperma 77 



Ambrosia artemisifolia 124 



Xerophytes : 



Celtis pallida 1 



Covillea tridentia 2 



Fouquieria splendens 7 



Tissues for Food Conduction and Storage. — The medullary 

 ray is composed of two kinds of cells, some with rather thick 



1. Bot. Gazette. June, 1905, pp. 396-408. 

 2-Univ. Sci. Bull.. Vol. V. No. 11. 



