AGE AT WHICH PLANTS CAN BEAK FRUIT. 93 



in biennials a longer period is required before tbis condition is 

 arrived at ; and in sbrubs and trees a still greater age must be 

 acquired. The American Aloe will not flower before it is thirty 

 years old, under the most favourable conditions ; and, under 

 unfavourable circumstances, the age at which it fructifies is so 

 much increased as to have given rise to the vulgar behef that 

 it flowers only after a hundred years. This curious subject has 

 been little investigated, and we Jiave no comparative state- 

 ments of the ages at which different species begin to bear ; but 

 the fact is certain. It is often, however, in the power of man 

 to advance or retard these periods artificially. Whatever pro- 

 duces excessive vigour in plants is favourable to the formation 

 of leaf-buds, and unfavourable to the production of flower-buds ; 

 while, on the other iand, such circumstances as tend to 

 diminish luxuriance, and to check rapid vegetation, without 

 affecting the health of the individual, are more favourable to 

 the production of flower-buds than of leaf-buds. Thus, a plant 

 in a sterile soil and exposed situation flowers sooner and more 

 abundantly than one in a rich and shaded place ; young vigorous 

 -plants flower later and less abundantly than old ones. In 

 India and China fruit-trees are made to bear by cutting their 

 roots, or exposing them periodically to dryness ; and in this 

 •country the same practice is observed, especially with the Fig 

 tree. An apparent exception to this law is found in the fact 

 that a seedling fruit-tree may be made, by grafting upon an 

 old stock, to bear flowers at an earlier age than it otherwise 

 would have done ; for the effect of grafting it thus is certainly 

 tiot to render it less vigorous, but the contrary. But it is 

 probable that aU these facts arise out of one common law, which 

 is, that the period when a plant begins to flower depends upon 

 the presence in its system of a Sufficient quantity of secreted 

 matter fit for the maintenance of the flowers when produced. 

 Under ordinary circumstances, a considerable part of all the 

 nutritious secretions elaborated by the leaves are expended in 

 the production of new leaves ; but after a time, a greater supply 

 is formed than the leaves require, and the residue collects in 

 the system ; as soon as this residue has arrived at the necessary 

 amount, flowers may begin to form. If the sterile branch 



