DICOTYLEDONOUS (EXOGENOUS) STEMS. ()5 



the bark from its subjacent wood-layers, but which is now, 

 as a fluid organically distinct from the surrounding tissues, 

 generally admitted as non-existent.* That the alburnum and 

 inner layer of bark are horizontally continuous at all times, we 

 are, I apprehend, correct in concluding no longer mere hypothesis, 

 but established fact, and, with our present efficient means of obser- 

 vation, of ready demonstration. The copious fluid investment 

 of the alburnum, discovered on removal of the bark in spring, 

 is occasioned, doubtless, by the rupture of the thin-walled and de- 

 licate cells of the zone intervening between the alburnum and 

 bark, the true cambium layer (Couche generatrice, verdiclcungs- 

 ring, d'C.J 



This imperfect apprehension of the true nature of that zone in 

 which the process of cell-division takes place, appears to have 

 been shared by the eminent French physiologist, Gaudichaud. 

 But the main question at issue between this observer and Tre- 

 cul — between, indeed, Gaudichaud and some of our most eminent 

 phytotomists, although it involved distinct and difl'ering views of 

 the role of the cambium layer, yet hinged rather on the correct 

 solution of a phenomenon of which this generative plane is the 

 seat, and which by theorists has been variously interpreted; per- 

 haps we cannot better express it than in the words of Brongniart, 

 " Les bourgeons, les vaisseaux, et les feuilles, produisent-ils les 

 Jlhres et les vaisseaux du hois ou de V ecorce ; ou Men, elaborent 

 Us seulement le fiuid nourricier ou seve descendante qui dois 

 alimenter ces tissus.^^f 



Our first business was to institute experiments more or 

 less in repetition of those of Trecul, devised Ayith a view to 

 afi'ord a satisfactory solution of this question. The chief fea- 

 ture in these experiments was the imposition of certain condi- 

 tions on the Dicotyledonous stem, whereby the possibility of ver- 

 tical continuity of the newly-forming tissues with the leaves, tfec. 

 above, was absolutely cut off". These conditions were attained 

 by annular decortications and notches. The detail of several of 



*One of the most recent publications, in which the case is correctly stated, as I sup- 

 pose, is the Microge- Dictionary (Griffith & Hcnfrey), p. 107. 

 t Annales, 3 Sen, vol. xviii, p. 58. 



