SHOOTS 
75 
52. The rootstock type, This is prob- 
ably the most common form of subter- 
ranean stem. It is elongated, as are foli- 
age stems, and hence the scale leaves 
are well separated. It is prominently 
used for food storage, and is also admirably 
adapted for subterranean migration (see 
Fig. 68). It can do for the plant, in the 
way of migration, what prostrate foliage- 
bearing stems do, and is in a more protected 
position. Advancing beneath the ground, 
it sends up a succession of branches 
to the surface. It is a very efficient 
method for the "spreading" of plants, 
and is extensively used by grasses in cov- 
ering areas and forming turf. The persist- 
ent continuance of the worst weeds is often 
due to this habit (see Figs. 69, 70). It 
is impossible 
FIG. 65. Branch buds 
of elm. Three buds 
(K) with their over- 
lapping scales are 
shown, each just 
above the scar (6) 
of an old leaf. 
After BEHREN?. 
FIG. 66. A bulb, made up of overlap- 
ping scales, which are fleshy on an( j vigorous activity, 
account of food storage. After 
to remove 
all of the 
indefinitely 
branchin g 
rootstocks 
from the soil, 
and any fragments that remain 
are able to send up fresh crops 
of aerial branches. 
53. Alternation of rest and 
activity. In all of the three 
stem types just mentioned, it 
is important to note that they 
are associated with a remark- 
able alternation between rest 
From 
GRAY. 
the branch buds the new leaves 
