188 
JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
curvature downwards at once commences. If the tip be broken 
off, gravity ceases to act upon the root, and fresh roots have to 
be made, and consequently dangerous delays may occur in trans¬ 
planting seedlings. 
Boots and their Functions .—The absorbing surface is con¬ 
fined to a certain bub short distance immediately behind the 
apex, and consists of the delicate epidermal surface with its 
root-hairs if present. This is easily proved by a simple experi¬ 
ment of placing a Radish plant with its tip only in water; the 
leaves, &c., will keep quite fresh. If, however, it be so bent, e.g ., 
in a tumbler of water, as to submerge the greater part of the 
root, leaving the tip outside, the foliage will soon wither. All 
these facts demonstrate the vital importance of keeping as many 
as possible of the extreme tips of the roots intact, when trans¬ 
planting herbs or shrubs. Another physiological fact about 
roots is their occasional production of buds. Roots and stems 
are fundamentally the same thing ; but, as a rule, stems produce 
buds, because they grow in air and light. Roots, as a rule, do 
not; but if they be superficial, as in many trees, they frequently 
assume this function. Many plants have acquired the habit of 
doing it habitually. Elm trees by a road side in time make a 
perfect hedge over a superficial root. Raspberry roots have the 
permanent habit of throwing up buds. So that if buds are 
required from roots, they can be stimulated to bear them, as 
gardeners have discovered it to be possible in Peaches, Maclura , 
Paulownia, &c. 
Leaves and their Functions .—The two chief functions specially 
characteristic of leaves and other green parts are transpiration 
and assimilation ; for leaves are, so to say, the breathing, digest¬ 
ing, and perspiring organs of plants. To carry these functions 
on satisfactorily, cleanliness of the surface is desirable, for they 
are executed by means of minute pores, or stomates, in the 
epidermis. These two functions depend upon light; but before 
assimilation can be carried on at all, it is necessary for the leaf 
to be green. This can be effected only by light in ordinary 
plants. Light is compounded of many rays—such as the 
invisible, but sensible, heat rays, the ultra-violet invisible rays, 
and the intermediate coloured rays visible to our eyes. These 
range from red through yellow, green, and blue to violet, with 
intermediate mixtures, It is found that light of any colour will 
