PLANT NUTRITION. 39 
ferences of form. We have already alluded to some of 
these differences, according as the stem is above or below 
ground, covered with mere scale-leaves, or bedecked like 
a timber tree with true leaves. The pasture grasses and 
cereals have almost all hollow erect, knotted stems ; the 
sedges, which resemble the grasses so much, have mostly 
angular unjointed stems. The clovers have a thick stock 
giving off branches which trail along the ground, The 
hop coils around the supporting pole by means of its 
climbing stem. Then there are the differences in dura- 
tion associated with corresponding differences in texture 
and internal construction. There are the so-called’ 
annual stems, which would lie down, even if they were 
not cut down after one season’s growth; there are the 
perennial stems, like those of fruit or timber trees or 
shrubs, and the duration of whose existence may be 
counted by years, and often by centuries. Then, again, 
there is an intermediate class of cases where the root- 
stock remains below-ground for a period long enough to 
justify the term perennial, while the branches or shoots 
die down after the seed is ripe, or are killed to the ground 
by a touch of frost, as in the common nettles. 
Buds, Branches, Tubers, Etc.—The branches or sub- 
divisions of a stem originate as buds or “‘ eyes,” which 
are placed at the free ends of the stem or of its branches, 
or which originate from the side of the stem or branch, 
in what is called the “‘axil” of a leaf, or of a leaf-scale, 
the axil being the angle formed by the base of the leaf at 
the point where it springs from the stem. The traces of 
their origin are often lost as the plant grows, but the 
rule is, as it has been stated, subject to a few exceptions 
of no moment for our present purpose. It is not usual 
for a bud to be borne in the axil of every leaf, far from 
it, but this is the place where the side-buds when they do 
exist are almost sure to be found, The shoots which 
