THE STEM 91 
nature becomes apparent only after a careful examination. 
But while the chief function of underground stems is the 
storage of nourishment, they serve other purposes also. In 
plants requiring a great deal of moisture, 
like the ferns, and in others growing in dry 
places and needing to husband moisture 
carefully, like the blackberry lily, under- 
ground stems may be useful in preventing 
the too rapid evaporation that would take 
place through aérial stems. Defense against N, 
frost, cold, heat, and other dangers, as well, 
as quickness of propagation, are also attained 
or assisted by this means. 
105. Rootstocks and rhizomes.— From a 
prostrate stem like that shown in Fig. 95 to a a 
7 # ? ‘ Fria. 104. — Root- 
creeping rootstock like the one in Fig. 104, the stock of creeping 
transition is so easy that we find no difficulty Pane 275s 
in accounting for it. From the prostrate rootstock to the 
thickened storage rhizome (Fig. 105) of such plants as the iris, 
puccoon, bulrush, and Solomon’s-seal, is a longer step, but 
the bud with its leaf scales at the growing tip, a, the remains 
of the flower stem at the node, b, and the roots from the under 
6 surface sufficiently indicate its na- 
ture. The peculiar scars from which 
Q@ the Solomon’s seal takes its name 
mp are caused by the falling away 
Fig. 105.— Rhizome of Sol. C20h year of the flowering stem 
omon’s-seal: u, growing bud at of the season after its work is done, 
the ip ib: remains of the Past leaving behind the node of the un- 
of old stems. (After Gray.)  derground stem from which it orig- 
inated. In this way the rhizome lives on indefinitely, 
growing and increasing at one end as fast as it dies at 
the other. Test a little of the substance of the rhizome 
with iodine. Of what does it consist? Of what use is it 
to the plant? 
106. The tuber. — A still further thickening and shorten- 
gpl, £7 
ema sete 
