HOW TO STEIKB LEAVES. 277 



keeping the soil in which they were inserted continually wet ; 

 that those of July, August, and November struck best, and the 

 spring leaves worst. Mr. Knight, who made the leaves of the 

 common Peppermint grow, planted them in the early part of 

 summer, in small pots, in heat, under glass. Bits of Water- 

 cress leaves wiU strike root freely ; but it is only such as float 

 on the water. -The common way of converting succulent leaves 

 into plants is to place them on damp sand, under a bell-glass, 

 or without one, according to the nature of the leaf. These 

 practical details show that water is employed to replace the 

 sap on which leaves usually subsist. But other points are of 

 equal importance. 



Of thes'e, the first. is to select leaves at the right season: if 

 they are too young, they are not capable of feeding themselves 

 when sundered from -their parent ; if too old, their vigour is 

 impaired, and their vitality on the wane. . Skilful propagators 

 therefore take care to employ leaves .fully grown, but not 

 beginning to change colour; such as those found about the 

 middle of a branch in full vigour. 



A second precaution is the application of more warmth than 

 the leaves had been previously subject to. All the vital 

 energies of plants are increased under the influence of heat, 

 and in a case of this Bort nothing must be neglected that will 

 Stimulate the flagging powers of life. Aided by warmth the 

 leaves form their secretions faster^ generate their cellular matter 

 faster, and so form their callus sooner. Quickness of actioii 

 is of great importance in such an operation as leaf-strikihg. 



A third condition will be perfect equability of moisture ; the 

 leaf must not be expected to feed by the end of its stalk 

 exclusively, but food must be presented to its whole surface ; 

 not, however, too much nor too little. If too much, the ,leaf 

 will be unable to digest it, and will perish of repletion;, if too 

 little, the cells wiU collapse, their excitability will be impaired, 

 and there is an end of the experiment. Herein consists^the 

 main difficulty of the operation, for leaves have very different 

 powers of taking in food and 'digesting it ; and nothing but 

 experience can adjust exterior conditions to the peculiar 

 organization of species. 



