THE STEM . 51 
buried in the soil. These underground stems are distin- 
guished from roots (a) by their having leaves and buds ; 
(b) by the fact of their being continuous with that part of 
the plant which bears foliage leaves; and (c) by their 
arising in the axils of leaves. The following common types 
ofundergroundstems 
‘or shoots may now 
be considered: tu- 
bers, bulbs, and 
rhizomes. 
Tubers. <A tuber 
is an underground 
shoot consisting of a 
swollen stem. The 
Fig. 41.—(a) Old tubers. (b) Young tubers. . ; 
ic} Roots: | Potato-tuber is such 
a shoot; its eyes 
are buds occurring in the axils of very small leaves. The 
tubers, moreover, are continuous with the stem which 
rises through the soil into the air. If developed above 
the ground the tubers themselves will bear foliage leaves. 
The roots of the Potato, for the most part, spring from 
the lower parts of those por- 
tions of the stem which are 
not swollen. 
Bulbs. A bulb is an 
underground shoot which 
consists of a short plate-like 
stem surmounted by thick 
fleshy leaves. If a Lily bulb 
be cut down through the 
centre towards the root, its 
structure can readily be seen. 
Notice the buds, recognisable 
. : Fig. 42.—Bulb of Lily. 
by their enveloping leaves, a, Bute: b, Plate, the tree erat, 
