754 Marvels of the Universe 
the soft new shoots become limp, 
and in a long continued drought 
shrivel up or fall off. Leaves, 
under the conditions prevailing 
where the Cactus grows, are a dan- 
gerous possession on this account ; 
and so the Cactus has learned to 
do without them. The vegetative 
body that ordinary plants spread 
out in the form of stems, branches 
and leaves, offers in that form so 
enormous a surface for evapora- 
tion that the Cactus has had to 
concentrate it all into a globular 
or cylindrical form, so that the 
external surface is reduced to a 
minimum. Then all the cells and 
tissues of which it is constructed 
have had to be provided with 
Photo by] LS. LZ. Bastin. 
A MAMMILLARIA. extra thick walls, so that trans- 
A second example, in which the longer spines are more fusion of fluids from one to the 
evident. 
other and to the exterior shall not 
be so rapid as in other plants. Having given up the luxury of leaves, the entire surface of this 
globular or cylindrical body has had to carry out the functions of the leaves. So we find that the 
skin of the Cactus is always green and soft, and microscopical examination would show that it is 
provided with stomata—the breathing pores through which it takes in gaseous food, and gives off 
gases evolved in the process of nutrition. We have said the Cactus has given up leaves. Here we 
feel we must hedge a little: the 
statement is too sweeping and must 
be qualified. Leaves, as such, it is 
true, are not to be found, but they 
are present in a changed form. 
They have all been converted into 
spines and prickles ; some of them 
stout and long, others fine as finest 
hair, but all ending in long points 
of almost microscopic fineness. 
Often from every cushion of short, 
fine spines there arise several 
spines of much greater length and 
standing out straight. Whilst the 
long spines are evidently designed 
to jab the muzzles of the larger 
mammals, the shorter ones would 
prevent smaller animals like mice 
Photo 5 TS. L. Sam from pushing their slender muzzles 
THE BROOM CACTUS. underneath the long spines and 
The plants photographed do not show the normal form, the ridges having Yo) getting a_ bite. It is a com- 
grown in such a way as to produce curved crests analogous to the familiar 
garden Cockscombs. mon practice for plants of many 
