1906] SPALDING—ABSORPTION OF WATER BY LEAVES 265 
one or two meters in height. These several species of Parkinsonia, 
Prosopis, and Acacia thrive well under the rather severe conditions 
to which they have become accustomed; they all retain, however, 
manifest traces of mesophytic habits, particularly in their choice of 
habitat. 
The species assigned to the third group, among which are Fou- 
quieria splendens, Holacantha Emoryi, Koerberlinia spinosa, and 
Zizyphus lycioides, present more striking modifications of form 
and structure than do any of the members of the preceding groups, 
and, though differing greatly among themselves, agree in possessing 
such conspicuous adaptations to xerophytic conditions as easily to 
rank next to members of the following biological group. 
The cacti are commonly taken to represent the extreme type 
of xerophytes, but notwithstanding various striking features com- 
mon to members of this order, there are essential differences of 
habit and adaptation, even between closely related species, ren- 
dering it quite impossible to generalize from the study of “typical 
forms” in the investigation of biological problems presented by 
them. 
The half-shrubby and herbaceous plants are much like those 
of other regions, exhibiting as a rule no structures that would be 
thought of as distinctively xerophytic, but accommodating them- 
selves to desert conditions by their habits, especially such as enable 
them to take advantage of periods favorable for rapid development 
and production of seeds. 
By way of first ascertaining whether any of the plants of these 
several groups absorb enough water through their leaves or inter- 
nodes to be readily detected by weighing, the following method 
was employed: A small branch with leaves functionally active, 
though often showing plainly the effects of long drouth, was severed 
and the cut end immediately covered with vaseline. In a few 
instances, which are specified, branches without leaves were used. 
The branch was then weighed and directly afterwards immersed 
in water, except at the cut end, for a definite time, usually about 
three hours. At the end of this period, after exposure to the open 
air long enough to be certain that the surface was fully dry, the 
branch was again weighed, and the increase of weight, if any, was 
