THE MORPHOLOGICAL COMPOSITION OF PLANTS. 39 



less and less compound, in proportion to their remoteness 

 from the main currents of sap; and that 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 which 

 cause growth are nearly equilibrated by the forces which 

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

 about to be 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 

 contrasts are still more marked between triple leaves and 

 simple leaves. This connection of decreasing size with de- 

 creasing composition, is conspicuous in the series of figures: 

 the differences 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 circum- 

 stances, as variations in the amounts of sunshine, or of rain, 

 or of matter supplied 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- 



