304 
THE FLOBAL WOELD AND GABDEN GUIDE. 
that the mean temperature of the summer there were 70°— which is, 
we believe, about the truth — the sate course for the gardener to take 
would be to plunge his cutting into soil warmed up to 75°. 
The action of light and moisture upon cuttings is hardly inferior 
to that of heat. Let us glance at their action separately. The 
moment light strikes a green plant, it excites perspiration. Let us 
imagine that a cutting weighed twenty at daybreak. The uninter- 
rupted action of light upon it during the day would perhaps reduce 
its weight to five, unless it is supplied with water to replace that 
which the sunlight drives off. The effect of this would, of course, 
be to kill it. 
But such a result does not often happen to rooted plants, because 
they are able to suck fluid out of the earth as fast as the sun drives 
it off from the leaves, and the circulation of the plant is active 
enough to prevent any part from being exhausted of fluid. If it is 
not sufficiently active, then we have leaves withered at the end, or 
branches struck with dryness. But a cutting, having no roots, is 
unable to contend against the sun’s influence, and therefore it must 
be shaded ; for, as we cannot make it feed, we must prevent its 
wanting food. Thus, in tropical countries we learn from Mr. 
Neumann that cuttings are struck in sheds shaded by straw, and 
watered occasionally ; with us the same point is also gained by 
cutting off the leaves, or a part of them, for they are the chief 
perspiring organs. But there is this disadvantage in cutting off the 
access of light, that roots are formed more rapidly, when cuttings are 
exposed to light, than when they are shaded, provided they can be kept 
alive. It is, therefore, a great problem to determine how much light 
a cutting will endure with impunity. The power of bearing light 
varies from species to species, and is only to be determined by 
experience. One plant fades presently, because its powers of per- 
spiration are very great, as is the case with the young shoots of most 
species of herbaceous and shrubby plants ; but as they grow older 
the loss by perspiration diminishes, because their thickened skin 
opposes a mechanical obstacle, and they can bear more light. It 
would therefore seem, at first sight, that ripened cuttings must, in all 
cases, be preferable to those which are young and tender. Certainly, 
they are less liable to die quickly ; but they are also much more 
unwilling to root quickly. In fact, notwithstanding the difficulty of 
keeping very youug cuttings alive, they present the only means of 
striking very difficult species, such, according to Mr. Neumann, as 
the Cashew, the Mahogany, and the Litchie. We may lay it down 
as a certain rule that the power of rooting is always greatest in all 
cuttings when they are first pushing, provided they have light. The 
misfortune is, that they are so extremely perishable at that time. 
Water is our aid in this case. It is true that the sun’s influence 
can have no injurious tendency so long as the roots can drink and 
the system digest as fast as the surface perspires ; and that the 
reverse is fatal. But the whole surface of a plant absorbs as well as 
evaporates, and the younger it is the more it absorbs, it is therefore 
possible to give plants drink by their leaves ; and if this is done with 
skill, the bad influence of the sun is prevented. In that case the 
