374 MR. H. M. CHIBBER ON THE MORPHOLOGY 
ares. The parenchyma-ring outside the collenchyma is only two or three 
cells deep. This ring also is characterized by an abundance of the secretory 
cells. 
The epidermis is best studied in a surface-section. The cells are very 
unequal. The lateral walls are straight. The hairy covering is composed of 
hydathodes and simple hairs. The latter are either unicellular or uniseriate: 
multicellular (Pl. 18. fig. 23). They are either mere bosses or short conical 
structures, Their breadth at the base is 12 р; their length varies from 10 to 
50u. When multicellular, the number of cells is usually two or three. They 
are free from any crystalline contents or inerustations, When full-grown, 
they contain nothing beyond eell-sap. Their number is too small to form a 
definite covering or to impart to the surface any pilose appearance. The 
young stem is strigose, with short broken whitish lines. These lines mark 
the position of the stomata (PI. 18. fig. 24) ; they are of the same character 
as those on the leaf, but appear somewhat elongated when their long axis 
coincides with that of the stem. 
Stems: Structure after the Formation of Secondary Growth. 
А )/ Y 
Mucilage-Canals.—A fully-formed axis shows a central canal and about 
a dozen peripheral canals situated in the ground-tissue just outside the 
medullary bundles. They have a diameter of 250 ш. Occasionally the 
centre is occupied by two canals lying close to each other. 
Pith—The parenchyma of pith is made up of three elements :— 
(1) Ordinary parenehymatous cells, enclosing intercellular spaces. Their 
diameter in a transverse section measures about 45 ш. Their height is 
ariable, but it is often twice the breadth. Many of them contain definite 
single crystals or mere crystalline sand, or both, composed of calcium 
oxalate. (2) Stone-cells : These are freely and regularly scattered through 
the cellulose parenchyma. They have the same height as the latter, but 
have a distinctly larger diameter, it being 60 ш. Their walls are thickened 
to б ш. They have simple oval pits, which measure З р in breadth ; their 
length is variable, but it is generally double the breadth, 7. e. 6 p. The 
stone-cells do not form any definite groups. Towards the centre they may 
occur completely isolated ; towards the periphery, just within and abutting on 
the inner sclerenchymatous ring, they form a continuous zone about five cells 
broad. This sclerosed parenchyma encloses intercellular spaces, just like tho 
cellulose parenchyma. (3) Secretory cells: These are larger than those in 
the leaf, being about 50 ш across. About fifty of them may be seen in a 
transverse section. 
Medullary Bundles.—Of these there may be as many as twenty in an 
old piece about 9 millimetres in diameter. They are arranged in a sinuous 
ring, or they may be regarded- as arranged in two rings, an outer and an 
