310 MR. H. M. CHIBBER ON THE MORPHOLOGY 
veins principally traverse this region. The secretory cells also are present 
here. 
The entire assimilatory tissue is characterised by the presence of large 
amounts of calcium oxalate in the cells, both in the form of well-formed 
crystals and fine sand. The leaf is free from any structures like water-pores, 
chalk-glands, spicular cells, or storage tracheids. 
Relative development of the Aqueous and Assimilatory Tissues.—The aqueous 
tissue constituted by the hypoderma and epidermis on either side is made up 
of five tiers or layers of cells altogether. In a fully developed leaf, which 
was 222 y thick, the upper aqueous tissue measured 63 ш and the lower 54 и. 
This left 105 u to the assimilatory tissue, of which the palisade measured 40 д 
and the spongy tissue 05 ш. Thus aqueous and assimilatory tissues stood at 
117 and 105,4 respectively. Hence the two may roughly be said to 
contribute equally to form the thickness of the adult leaf. 
On examining a young leaf, it was found that these proportions do not 
hold good (Pl. 19. fig. 35). There the aqueous tissue was noticed to be much 
nearer its full size than the assimilatory tissue, in which, on account of absence 
of elongation in the palisade-cells, the two layers, palisade and spongy, 
could not be differentiated. The actual figures are given below :— 
Upper aqueous tissue 51 ш; assimilatory tissue 63 д; lower aqueous tissue 
42 ш; entire thickness of the leaf 156 ш; entire aqueous tissue 93 д. 
Midrib.—A section of the midrib taken before it gives off the last or 
uppermost two secondary ribs is traversed by three large and a variable 
number (0 to 4) of smaller vascular bundles, all arranged in a crescent. The 
vessels have sealariform markings. There is a large mucilage-canal lying 
above the central bundle. It may measure 150 p across. The hypoderma 
of the blade is here substituted by collenehyma. A section of the midrib 
after it has given off all the secondary ribs shows only a single bundle. 
The mucilage-canal persists within an inch or two of the leaf-apex. 
Secondary Veins.— These. project freely on the under side of the leaf. 
A section of one of them agrees with that of the midrib taken at a point 
above the origin of the secondaries, with the exception that the mucilage-canal 
is absent in the secondary vein. 
Finer Veins,—The finer veins are embedded in the spongy parenchyma. 
They are not vertically transcurrent by any specialised tissue. They ulti- 
mately lose themselves in fine terminations that end freely. The extremity 
is formed by one or more fusiform tracheids ensheathed by short rectangular 
thin-walled cells. These cells, further away from the termination, give place 
to much elongated thin-walled cells forming a very distinct aqueous sheath to 
the veins. The tracheids are very variable in form. It is not unusual to 
find one of them forming a three-rayed star at a junction of three veins 
(PL. 18. fig. 25). 
The precise disposition of the terminals and the value of this character in 
