SOIL RELATIONS OF DESERT PLANTS. 89 
not more than ro cm. below the surface of the ground. There are therefore two 
noticeable characteristics of the root-system of Echinocactus wislizen1, namely, 
the roots are slender throughout their entire course and they are superficially 
placed. 
The roots of Cereus giganteus, on the other hand, in form and position, 
and perhaps in extent and branching also, are very different from those 
of Echinocactus. Fig. 2 presents the root-system of a Cereus giganteus, 
about 1 meter high, which was growing 200 meters west of the Echinocac- 
tus just described. Four main roots were observed to arise from the base 
of the plant. Very soon after leaving the plant the roots branched. 
One branch, whose later history could not be traced, struck directly 
downward, and the 
ieee ie SG 
less horizontal course. Pe esterase as 
The latter branched at hokage PIS a a a 
intervals, although 5 Ae aa 
perhaps not so fre- eg seed dale ee ae 
Fa a Hip 
quently as those of 
Echinocactus, and ex- 
tended,in one instance 
at least, over 1 meter 
from the plant’s base. 
How much farther the 
root reached could not 
be learned because of 
its fragility and the 
small size of the distal 
branches. The super- 
ficial portion of the 
root-system of Cereus 
giganteus Was more 
deeply placed than 
were the roots of Echi- 
nocactus, and, owing 
to the fact that these 
parts were not so densely branched, the ground included by them was 
not so thoroughly occupied. However, in one characteristic which is 
of interest to note, but the significance of which I have not investi- 
gated, the superficial roots of the two forms are alike, namely, the longer 
roots and the greatest number of roots are situated on the uphill side of 
the respective plants. This peculiarity is shown in the two figures. In 
fig. 3 the uphill side isto the right, and in fig. 2 it is at the top of the sketch. 
It is to be seen of course that the various types of roots also present 
the additional feature of varying temperature relations between the 











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Fic. 3.—Root-system of Echinocactus wislizent. 
meale: y unit = 1 toot: 
