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 



