Marvels of the 
different families, when growing in dry places 
where nutritive vegetation is scarce, to protect 
themselves from being eaten by turning leaves 
or shoots into spines or thorns. Examples that 
come readily to mind are the Acacias, and our 
own Furze, Blackthorn and Hawthorn. 
Imagine a herbivorous animal parched with 
thirst, and knowing, perhaps, by its sense of 
smell that the plump Cactus has its tissues full 
of cool liquid. He rushes at it to take a bite of 
the succulent flesh. But before his teeth can 
reach the rind his tender lips and tongue are 
pierced by hundreds of the needles, and he 
retires, howling with pain. It is only by occa- 
sional experiments of this sort that animals have 
learned that it is dangerous to attack such 
plants, and the experience goes into the stock 
of memories that passes by inheritance from 
generation to generation and commonly goes 
under the name of instinct. 
With a dry, loose surface there is often a fair 
amount of moisture in the subsoil, and the Cacti 
have long roots to send down on explorations for 
water. Even where there is very little buried 
moisture, there is, of course, need for an exten- 
sive root system to find what little is available. 
Many of the Cacti are boldly sculptured into 
The 
ridges bear cushions at regular intervals, and 
alternate thick ridges and deep grooves. 
these are surmounted by rosettes of spines. In 
some the spines are supplemented by long, white 
hairs, which give the plants so venerable an 
appearance, that one species in particular (shown 
on page 750) is known as the Old Man Cactus. 
These hairs have a protective function different 
from that of the spines—which also are present 
—for they tend to keep the surface cool, and 
so minimize the loss of moisture through 
evaporation. 
We must not get our notion of the Cacti 
from the diminutive plants in tiny pots that are 
sold for conservatory decoration. These are 
often mere rooted offshoots from plants that 
grow to a considerable size. A better idea of size 
may be obtained from the view of a Cactus 
garden in California (page 753), where a 
number of different species are seen growing 
side by side. The tall, upright shafts belong to 
a species of Torch-Thistle, or Cereus, one of 
Photo by] 
Universe 
155 
[hE J. Wallis. 
TORCH-THISTLE 
Many species of Torch-Thistle attain a great height. The 
character of their protecting spines is well shown in this 
photo. 
54 
