90 PRACTICAL COURSE IN BOTANY 
is so much used for decoration. 
The delicate green blades are 
merely altered stems, shortened 
and flattened to simulate leaves. 
102. Weapons of defense. — 
Conspicuous examples of these 
are the bristling thorns of the 
honey locust. Is their frequent 
branching any indication of their 
real nature? Does it prove any- 
thing, or must you look for other 
evidence? What further indi- 
cations might you expect to 
Fie. 102.— Thorn branches of : . 
Holocantha Emoryi, a plant growing find, if they are true branching 
asa stems? (100.) On old haw, 
plum, crab, and pear trees, stems can be found in all stages 
of transition, from stubby, ill-developed branches, to well- 
defined thorns. 
103. Storage of nourishment. — This is 
one of the most frequent causes of modifi- 
cation in both roots and stems. Of stems 
that grow above ground, the sugar cane 
probably comes first in economic importance 
on this account. In hot, arid regions, where 
the moisture drawn from the earth would, 
during prolonged drought, be too rapidly 
dissipated by an expanded surface of leaves, 
the whole plant, as in the case of the cactus, ; 
is sometimes compacted into a greatly thick- Ox 
ened stem, which fills the triple office of leaf, a 
stalk, and water reservoir. ’ dV >) 
Y 3 
(1 \ 
It is in these that the storage of nourishment — Fre. 103.—Melon 
: cactus, showing 
most frequently takes place, and the modi- pete daniel 
fications that stems undergo for this purpose _ stem for the storage 
i . d tion of 
are in some cases so great that their real ‘oistum, 
\p 
104. The uses of underground stems. — 
