ON THE WATER-CONDUCTING SYSTEMS OF SOME 
DESERT PLANTS.* 
W. A. CANNON. 
(WITH TEN FIGURES) 
A STATEMENT by VOLKENS® to the effect that the ducts of the 
stems of the shrubs and trees of the Egyptian-Arabian deserts are 
relatively poorly developed led to an examination of these elements 
in the shrubs and trees which are growing within reach of the Desert 
Botanical Laboratory. It appeared at once that our native plants 
are not poor in water-conducting tissue; on the contrary they are 
very well provided for in this regard, and I cast about for some means 
of expressing this condition of affairs from a comparative standpoint. 
It was especially desired to compare these plants with those of the 
deserts of Egypt and Arabia, but since the direct comparison was 
impracticable, because VOLKENS does not give exact data, I have 
sought a way out of the difficulty by using irrigated desert plants 
of the species studied as controls. I assume that the desert plants 
if provided with an abundance of water are for practical purposes 
mesophytes, and if VoLKENs had in mind the plants of middle Europe, 
Which might well have been the case, we have in this roundabout 
Manner a means of instituting the desired comparison. Aside from 
this, the great difference in the development of the conductive tissue 
between desert forms that have been irrigated and those that have 
not is of considerable interest in itself. 
THE PLANTS STUDIED. 
This study includes as many of the native desert trees and shrubs 
as are readily obtained, and also such as have been irrigated in various 
places in whatever manner or degree. These are the hackberry 
(Celtis pallida), the creosote bush (Covillea tridentata), the candle 
bush or ocotillo (Fouquieria splendens), and a relative of the cruci- 
*Papers from the Desert Botanical Laboratory of the Carnegie Institution. 
No. 12, 
* VOLKENS, G., Flora der iigyptisch-arabischen Wiiste, p. 82. 
905] 307 
