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 but 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 w T ater, 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, Madura, 

 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 founci that light of any colour will 



