Delf— Transpiration in Succulent Plants. 433 
which I have made, the loss per unit area of the detached leaves was un- 
doubtedly greater than that of attached similar leaves taken at the same 
time, under the same conditions. My experiments, however, were generally 
for much shorter periods of time, lasting from one to eight hours instead of 
several days, as did Pringsheim’s. In the case of Mesenibryanthemum ediile 
a shoot and an adult detached leaf, both sealed at the cut end, were weighed 
at intervals for three weeks. Throughout that time the loss in water per 
unit area of the detached adult leaf was much greater than that of the 
shoot with which it was compared. In the other cases examined by me, 
where the same is true, pairs of similar shoots were chosen and the tran- 
spiration per sq. dm. of a whole shoot compared with that of the lowest leaf 
of the control shoot detached from its stem. In every case loss from evapora- 
tion at the cut surface was prevented by sealing over with an adhesive wax 
mixture. In every case the transpiration of the detached leaf per unit area 
was greater than that of the attached ones. 
Whatever be the explanation, however, of this conservation of water in 
the plant, there is no doubt that it may be of great oecological value, as 
Pringsheim points out, not only in enabling the plant to withstand long 
periods of drought without injury to the growing point, but also in providing 
a means of vegetative reproduction ; for in many cases the exhaustion of the 
water supply of older parts causes the death of the lower parts ; the apex 
then continues its growth, and often roots freely, and becomes independent 
in some more favourable spot. This is seen in many species of Sedum , Mes- 
embryanthemum , Crassida , Rhipsalis , Cassytka, and many others. The ease 
with which adventitious roots form in these examples, however, varies 
greatly. In Sedum one or more adventitious rootlets regularly form, even 
in very dry air, just above the axil of the leaf, when each leaf is about half 
depleted. In M. edule roots are formed, but much less readily, and in 
M. crystallinum often not until many weeks have passed. In mesophytic 
plants the advantage is less obvious, for they have less power of storing 
water and often none of rooting from the apex ; but the greater transpiration 
of the younger, less protected leaves may be, at least in part, compensated 
by the water supply from the older ones. 
(y) The Conducting System. 
There is no doubt that the means of water conduction in a plant 
stands in close relation to the rate of transpiration. In general, the greater 
the amount of transpiration the larger will be the number and size of 
the conducting elements in the stem and root. Jost found that by cut- 
ting off the leaves and buds of seedlings of Phaseolus multiflorus and 
other plants, the vascular bundles, and especially the water-conducting 
elements, remained in a rudimentary condition. He interpreted this as 
