STEMS 61 
the skunk-cabbage, owe their early-blooming habit to richly 
stored underground stems of some kind, or to thick, 
fleshy roots. 
77. Condensed Stems.— The plants of desert regions 
require, above all, protection from the extreme dryness of 
the surrounding air, and, usually, from the excessive heat 
of the sun. Accordingly many desert 
plants are found quite destitute of 
ordinary foliage, exposing to the air 
only a small surface. In the melon- 
cactuses (Fig. 81) the stem appears 
reduced to the shape in which the 
least possible surface is presented by 
a plant of given bulk, — that is, in a 
globular form. Other cactuses are 
more or less cylindrical or prismatic, 
while still others consist of flattened 
joints; but all agree in offering much 
less area to the sun and air than is 
exposed by an ordinary leafy plant. ea ae er 
78. Leaf-like Stems. — The flattened “co tion of = Onion 
stems of some kinds of cactus (espe- Leaf. 
cially the common, showy Phyllocactus) sca, thickened base of 
are sufficiently like fleshy leaves, with a de tend 
their dark green color and imitation of leaf; i, blade of 
of a midrib, to pass for leaves. ‘There i ae HS in- 
are, however, a good many cases in 
which the stem takes on a more strikingly leaf-like form. 
The common asparagus sends up in spring shoots that bear 
large scales which are really reduced leaves. Later in the 
season, what seem like thread-like leaves cover the much- 
branched mature plant, but these green threads are actually 
