378 MR. H. M. CHIBBER ON THE MORPHOLOGY 
The formation of cork takes place in the outermost layer of the cortex. 
The cork-cells are radially compressed. Their radial walls measure 10 to 
12 u, tangent walls 20 to 24 u, and vertical walls 20 to 24 д. But the cells 
are often irregularly angular instead of rectangular, when the above 
measurements do not hold good. 
Lenticels—These arise by masses of cortical cells becoming secondarily 
merismetic. They soon enlarge, so as to rupture the regular cork-layer 
lying over them. The fully-formed lenticels cause oval concave depressions 
in the cortex, 
Roots. 
The general appearance of a transverse section of an old piece of root 
strongly reminds one of the stem of the woody Aristolochias, in which, 
“in the course of growth in thickness, broad secondary medullary rays are 
successively developed in the vascular bundles themselves, occasioning a 
dichotomous fission of the plates of wood and bast composing the vascular 
bundles? *. In the section reproduced (РІ. 19. fig. 57) there can be seen six 
primary medullary rays. The intervening xylem-plates have bifurcated once 
or twice. The centre of the section is oceupied by ligneous elements. 
The vascular elements are the same as those in the stem, and they have the 
same markings and peculiarities, 
The medullary rays are about twelve cells broad ; the cells are more regular 
than those in the stem. Here all the walls, including the radial ones, have 
somewhat the same length and almost the same level. Again, in the stem 
the radial walls exceeded the tangent walls. In the root the tangent walls 
exceed the radial ones, the former being 15 wand the latter 10 u. Their 
height is about 55 ш. The secretory cells, which are absent from the stem 
rays, are here present, though very sparingly. Another difference in the 
rays is constituted by the absence of lignification. 
The stele is limited hy a sclerenchymatous ring. It is usually one cell 
thick, but is here and there reinforced by an additional layer on the inner 
side. he continuity of the ring is broken at some points by solitary 
passage-cells, 7. e. unlignitied thin-walled cells (Pl. 18. fig. 32). 
The cortex is better developed than in the stem. Starch may be present 
hereas well. The secretory cells, which here attain a diameter of 60 p, occur, 
though somewhat sparingly ; their walls may be lignified or suberised. The 
cork-layer is also better developed here ; the component cells have the same 
size as in the stem. 
The Cell-Contents. 
The cell-contents, so far as revealed by the microscope, may be briefly 
noticed here. 
Starch-Grains.—The starch-grains range in size from less than one micron 
to nine microns in the longest diameter, and are roughly spherical in shape 
* Solereder, Syst. Anat. Dicot., Engl. Trans. p. 687, 
