338 
ON THE RIPENING OF THE GEOWTH OF PLANTS, ETC. 
consequently, comprehend the quality as well as tlie quantity of food ; and food over-rich, 
as well as food over-much, must alike be avoided. 
Exposure to drought is to a greater or less extent essential to the maturation of growth ; 
and this is necessary both in respect to the soil and the atmosphere. The effect of a due, 
that is, moderate, degree of dryness in the soil, is to prevent the absorption of any great 
proportion of watery matter ; and watery matters being those most readily absorbed, it is 
virtually a limitation of the quantity of food : this arrests growth in the sense of an 
extension or elongation of parts. Then if accompanied by a drying atmosphere, perspira- 
tion is accelerated, more watery matter is carried off, and organisable matter is more 
speedily prepared, and lodged in larger quantities in the parts destined to receive it. If 
soil drought is accompanied by the drying atmosphere, plants have then still less water 
to throw off, and, consequently, the process of elaboration and assimilation are so much the 
more readily carried on. Notwithstanding its advantages, however, exposure to drought 
at the root is rather a hazardous matter, with many races of pot-plants especially, for it is so 
very liable to pass beyond a safe limit, which limit the closest watchfulness will sometimes 
fail to observe. It ought, in fact, never to approach this limit too closely. With a dry 
atmosphere it is different. The effect of a drying atmosphere, as already observed, is to 
carry off the watery matter of the sap by a perspiratory process, and this is far less 
liable to reach an unsafe point, than is drying at the root. This too may, however, be 
carried too far, and then we have leaves dying at their tips and edges. This latter is 
exceedingly liable to occur in the case of plants not killed outright, nor stripped entirely 
of their foliage, if extreme drought at the root and in the atmosphere are coincident. 
The entire effect produced by a dry atmosphere, short of this destruction of the foliage, 
is conducive to elaboration of the sap, and to the maturation or ripening of the growth. 
Exposure to drought in the soil, so easily attainable in the case of potted plants kept under 
shelter, is simulated in the open ground by thorough draining. This operation, by removing 
all , superfluous or stagnant moisture, admits air into the soil, and prevents the roots 
absorbing an excess of water along with their food ; it does not, however, actually arrest 
absorption, which result is only brought about in very dry seasons by the desiccation of the 
soil owing to excessive and long-continued evaporation, which is an excess to be guarded 
against and counteracted as much as possible. Exposure to drought in the atmosphere is 
far less controllable, except in structures but sparingly ventilated; and hence it is in 
great measure that we see in dry warm seasons, not only the growth of out-door plants, 
but also that of all the hardier groups requiring shelter, becomes so much better ripened 
than it does in those which are cold and moist. The qualities of the all-pervading 
atmosphere cannot be changed, or to any material extent modified, on the large scale. 
Exposure to light — the degree variable — is an equally essential part of the maturative 
process ; it promotes certain chemical changes necessary to the perfect elaboration of the 
sap, and what is called the assimilating process, without vdiich elaboration and assimilation 
no perfect ripening or maturation takes place. Light is, however, the least controllable 
of the agents conducive to uiaturation. A bright or a dull season, for instance, makes all 
the difference in the ripening of fruit trees. 
But what are the leading objects of the maturation of the growth of plants as it regards 
artificial cultivation ? Undoubtedly the production of flowers and fruits. Wherever these 
objects are sought, maturation of the growth becomes all-important. The same process is, 
indeed, to some extent essential to the health and well-being of all the higher races of 
vegetables from their infancy onwards, but in a much slighter degree than is contemplated 
in this paper. For the production of blossoms, the precursors of fruit, thorough rijoening 
is indispensable. Flowers and fruit are formed out of that organisable or elaborated or 
assimilated matter which becomes accumulated in the plant, on its exposure, to a certain 
extent, to those agencies that have been pointed out as promoters of the ripening process ; 
and as this elaborated matter is only prepared under the influence of these agencies, they 
must have done their part before the production of flowers becomes possible. There are 
two antagonistic forces in plants : one tending towards mere vegetative growth, the increase 
of size in the individual, the development of stems and leaves ; the other tending towards 
