30 MORPHOLOGICAL DEVELOPMENT. 



and less compound, in proportion to their remoteness from the 

 main currents of sap ; and tha,t where an entire absence of 

 divisions or lobes is observed, it is on leaves within the 

 flower-bunch : at the place, that is, where the forces that 

 cause growth are nearly equilibrated by the forces that 

 oppose growth ; and where, as a consequence, gamogenesis is 

 about to set in (§ 78). Additional evidence that the degree 

 of nutrition determines the degree of composition of the leaf, 

 is furnished by the relative sizes of the leaves. Not only, on 

 the average, is the quintuple leaf much larger in its total area 

 than the triple leaf ; but the component leaflets of the one, are 

 usually much larger than those of the other. The like con- 

 trasts are still more marked between triple leaves and simple 

 leaves. This connexion of decreasing size with decreasing 

 composition, is conspicuous in the series of figures : the differ- 

 ences shown, being not nearly so great as may be frequently 

 observed. Confirmation -may be drawn from the fact, that 

 when the leading shoot is broken or arrested in its growth, 

 the shoots it gives off (provided they are given off after the 

 injury), and into which its checked currents of sap are thrown, 

 produce leaves of five leaflets, where ordinarily leaves of three 

 leaflets occur. Of course incidental circumstances, as varia- 

 tions in the amounts of sunshine, or of rain, or of matter sup- 

 plied to the roots, are ever producing changes in the state of 

 the plant as a whole ; and by thus affecting the nutrition of its 

 leaf-buds at the times of their formation, cause irregularities 

 in the relations of size and composition above described. But 

 taking these causes into account, it is abundantly manifest 

 that a leaf-bud of the bramble, will develop into a simple 

 leaf or into a leaf compounded in different degrees, according 

 to the quantity of assimilable matter brought to it at the 

 time when the rudiments of its structure are being fixed. 

 And on studying the habits of other plants — on observing 

 how annuals that have compound leaves, usually bear simple 

 leaves at the outset, when the assimilating surface is but 

 small ; and how, when compound-leaved plants in full growth 



