1906] SPALDING—ABSORPTION OF WATER BY LEAVES 273 
Covillea tridentata. 
The specimens of creosote bush selected for experiment were 
taken from four different sources, for the sake of securing material 
as different as practicable in regard to the amount of water in the 
tissues. Number 1 was from a bush growing near an irrigating 
ditch, where it had been abundantly supplied with water. Its 
leaves were large, dark green, and fresh, and numerous flower buds 
had been formed. Number 2 was from a plant growing on the 
mesa a few rods distant. Its leaves were smaller and lighter green, 
and in comparison with number 1 it was plainly a dry ground form, 
though it did not have the appearance of having suffered to any 
great extent from lack of water. Numbers 3 and 4 were from plants 
growing on the mesa, near the foot of the laboratory hill, where 
in a dry time the Covillea, the only shrub that keeps alive there, 
shows the effects of drouth very badly. Their leaves were still 
smaller and paler in color, those of number 4 especially, indicating by 
their minute size and other peculiarities a plant that had long lacked 
a sufficient supply of water. The contrast between this and the 
first member of the series was very striking. It should be stated, 
however, that none of the specimens were in quite so dried-up a 
condition as those employed early in November before the Decem- 
ber rains, which though meager—o.82 inch (21™™) thus far— 
had freshened vegetation to some extent. The dried-up leaves 
that were dying in November had been shed, and the leaves remain- 
ing on the bushes when the experiment was conducted, late in Decem- 
ber, were apparently in a vitally active condition. 
It will be noticed by reference to Table VIII that, precisely as 
in the case of Celtis, all the specimens of Covillea gained very little 
in weight as the result of wetting soon after they were cut. Num- 
ber 1, from the irrigated bush, gained least, and number 4, from 
the dry ground plant, gained most. After prolonged drying and 
again wetting, the gain was much greater than before, the greater 
gain in each case being made by number 4, which, as already stated, 
was from the most distinctively dry ground form. 
The deportment of number 1, from the robust, well-watered 
bush, is instructive, especially as it may throw light on the question 
as to whether leaf absorption is a normal process that takes place 
