1861.] on Tree Twigs, 359 



which extended down the outside of the tree to the ground, and 

 farther, to the extremities of tlie roots. The mode in which this 

 descending masonry was added, appeared to depend on the peculiar 

 functions of cambium ; and (the speaker believed) was as yet unex- 

 plained by botanists. 



Every leaf, besides forming this masonry all down the tree, pro- 

 tected a bud at the base of its own stalk. From this bud, unless 

 rendered abortive, a new shoot would spring next year. Now, suppos- 

 ing that out of the leaf-buds on each shoot of a pentagonal tree, only 

 five at its extremity or on its sides were permitted to develope them- 

 selves, even under this limitation the number of shoots developed from 

 a single one in the seventh year would be 78,125. The external form 

 of a healthily-grown tree at any period of its development was therefore 

 composed of a mass of sprays, whose vitality was approximately distri- 

 buted over the surface of the tree to an equal depth. The branches 

 beneath at once supported, and were fed by, this orbicular field, or 

 animated external garment of vegetation ; from every several leaf of 

 which, as from an innumerable multitude of small green fountains, the 

 streams of woody fibre descended, met, united as rivers do, and gathered 

 their full flood into the strength of the stem. 



The principal errors which had been committed by artists in 

 drawing trees had arisen from their regarding the bough as ramifying 

 irregularly, and somewhat losing in energy towards the extremity ; 

 whereas the real boughs threw their whole energy, and multiplied their 

 substance, towards the extremities, ranking themselves in more or less 

 cup-shaped tiers round the trunk, and forming a compact united surface 

 at the exterior of the tree. 



In the course of arrival at this form, the bough, throughout its 

 whole length, showed itself to be influenced by a force like that of an 

 animal's instinct. Its minor curves and angles were all subjected to 

 one strong ruling tendency and law of advance, dependent partly on 

 the aim of every shoot to raise itself upright, partly on the necessity 

 which each was under to yield due place to the neighbouring leaves, 

 and obtain for itself as much light and air as possible. It had indeed 

 been ascertained that vegetable tissue was liable to contraction and 

 expansion (under fixed mechanical conditions) by light, heat, moisture, 

 &c. But vegetable tissue in the living branch did not contract nor 

 expand under external influence alone. The principle of life mani- 

 fested itself either by contention with, or felicitous recognition of, 

 external force. It accepted with a visible, active, and apparently 

 joyful concurrence, the influences which led the bough towards its due 

 place in the economy of the tree ; and it obeyed reluctantly, partially, 

 and with distorted curvatures, those which forced it to violate the 

 typical organic form. The attention of painters of foliage had seldom 

 been drawn with suflficient accuracy to the lines either of branch curva- 

 ture, or leaf contour, as expressing these subtle laws of incipient voli- 

 tion ; but the relative merit of the great schools of figure-design might, 

 in absence of all other evidence, be determined, almost without error, 



