372 MR. H. M. CHIBBER ON THE MORPHOLOGY 
not always observed ; occasionally a solitary bundle may be found orientated 
at right angles to the normal position, so that the dividing-line between 
xylem and phloem forms a radius instead of a tangent, The larger bundles 
have a starch-sheath, which is incomplete on the inner or xylem side. It is 
one cell thick, and suggests the structure of the petiole to be schizostelic. 
The phloem is characterised by the presence of the secretory cells within 
its limits. 
The cells lying just outside the xylem and phloem ends of the bundle have 
definitely thickened walls, but no trace of lignification could be detected, A 
section through the initial or basal region of the petiole differs from that 
through the apical or characteristic region in the following points. 
There is a larger number of small bundles that are interealated between 
the principal ones. There may be a mucilage-canal for every major bundle, 
i.e., about seven of them; these lie in the same radius as the bundle, almost 
abutting on it on the xylem side. The bridges of ordinary cortical cells 
‘between the collenchyma-ares are widened into a second set of ares inter- 
calated between the former. The collenchyma on the upper side of the 
section is replaced by tabular parenchyma, the walls of which are thickened 
and the radial arrangement of which strongly reminds one of tabular cork- 
cells ; the walls, however, are of cellulose, This zone of tabular parenchyma 
is much deeper than the replaced collenchyma, being about twelve cells 
deep. 
Stems: Primary Structure. 
A transverse section near the apical region reveals the following points, 
To begin with the centre, this is occupied by a well-differentiated mucilage- 
anal (Pl. 19. fig. 36). Its lysigenous origin is clearly indicated at this 
stage by loose cells lying about in the cavity (РІ. 18. fig. 30). The cells 
bounding it do not form a distinet epithelium; they show some granules 
within their cavities besides mucilage. The mucilage is true gum, being 
completely soluble in water. It readily stains with mnethylene-blue. 
Next, there may be noticed the mucilage-canals lying in the peripheral 
part of the medulla. These, however, are slower to appear than the central 
canal, nor do they appear simultaneously. In the section reproduced 
(РІ. 19. fig. 36) four of them are well formed, in one the cavity is very 
narrow but distinct; while one more does not show any formation of 
cavity, but it is indicated only by. the group of cells, destined to form the 
canal, retaining their nuclei and possessing contents that stain deeply with 
methylene-blue or hematoxylin, Тһе same section shows in the medulla the 
secretory cells freely scattered throughout. These, however, are not so 
clearly differentiated as the mucilage-canals, for in the section we can make 
out three distinet mucilage-canals ; but the major part of it is free from any 
indication of the future numerous secretory cells, The section also indicates 
