30-4 THE ELOEAL WOELD AND GAEDEN GUIDE. 



that the mean temperature of the summer there were 70°— which is, 

 we believe, about the truth — the safe 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 

 unwillino- to root quickly. In fact, notwithstanding the difficulty of 

 keeping very young 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 





