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Reactions of the Petioles of P ter is aquilina. 
deeper seated. In addition to the reaction to phloroglucin given by the 
obviously thickened elements, a red coloration frequently occurs in the 
adjoining cortical tissue in which there appears to be no thickening, so 
that it is evident that lignification is produced to some extent in these 
tissues also. 
Fig. t. i. Diagrammatic transverse section of wound’area showing compensatory thickening of 
cortex, ii. Diagrammatic transverse section near middle of wound area shown in i. Note the 
spread of the thickened tissues in the neighbourhood of the vascular strands, iii. Small portion 
of i, showing the delignified sclerenchyma on the flank of the wound and its increased thickness, 
iv. A single cell (a) from iii, showing the stratification of the wall. v. A small portion of the 
thickened cortex in the vicinity of a bundle, vi. Remains of bundle ii. B, showing the thickened 
cells of the starch sheath, vii. Remains of bundle ii. C, showing thickening and in some cases 
elongation of cells of the starch sheath, viii. Portion of wounded petiole from which i and ii were 
cut, i being from the narrow end, ii from the broad end. i and ii x 12, iii x 350, iv x 650, v x 250, 
vi and vii x 500, viii x 1. scl. sub-epidermal sclerenchyma ; cor. thickened cortical cells. 
A second and more pronounced type of reaction which occurs fairly 
frequently is that of the radial elongation of the cortical cells in the wound 
area (Fig. 2, iv). This phenomenon is usually accompanied by an increase 
in the thickness of the cell-walls, as in the cases previously described. 
Between the two types of reaction, namely, thickening with elongation, and 
thickening alone, no sharp line of division can be drawn, since in many the 
more vigorous type of response occurs in the middle of the wound area 
whilst absent from the two ends. Moreover, there are instances in which 
a local patch of cortical parenchyma has elongated and become thickened, 
whilst throughout the rest of the wound no such elongation is manifest 
(Figs. 3, i ; 2, ii, c). Local growth of this character seems in no sense 
K 
