ra 
. 1906] SPALDING—ABSORPTION OF WATER BY LEAVES 281 
TABLE XIII. 
OPUNTIA VERSICOLOR. December 1904. 
. | Weight in| Loss or gain’ de 
No.| Date Time Pisano per cent. Conditions 
1 | Dec. 3 | 10:30 A.M. 116.390 
1355 P.M. |16.770 | 2.3 gain | See Table XII 
f | FE Ae. [16.580 7|o21 7? 
2 6 | 9:55 A.M. |10.640 
12:14 P.M. /10.850 | 2.0 gain 
3:02 10:630 | 2.0 loss 
3 10:30 A.M. | 8.115 
12:35 P.M. | 8.360 | 3.0 gain 
3:10 8.115 | 2.9 loss 
a gain of 2 to 3 percent. The specimens most shrunken with drouth 
were found to absorb water most rapidly. 
The rapid loss of water and the curiously close correspondence 
in each case between the percentages of gain and loss, suggest that 
in this species it is merely the tubercles that act as organs of absorp- 
tion, and notwithstanding the fact that the water absorbed is so 
promptly given off in a dry atmosphere, it appears probable that 
in a period of frequent light rains the continued absorption of water 
by the tubercles is precisely the necessary preparation for the develop- 
ment of the young shoot which presently follows. Meantime the 
different deportment of these two species of Opuntia as regards 
amounts of water absorbed, corresponding as it does with a marked 
difference in size of their tubercles, suggests the desirability of a 
more extended comparison of these structures in different cacti 
with reference to their marcas for absorption and the physiological 
value of the process. 
GROUP V. 
A discussion of the annuals and partly herbaceous perennials 
that have been referred to a fifth biological group, many of which, 
structurally at least, are not to be thought of as characteristic desert 
plants, does not fall within the limits of the present study. As 
already stated, as many of them as have been studied agree in 
promptly absorbing water when it is presented to their leaves and 
internodes, which, however, is given off so rapidly in dry air that 
it hardly seems possible that its absorption is of any utility. Cy. 
Table I, Encelia and Sphaeralcea. 
