"(19 INTRODUCTORY ESSAY. 
Very commonly we find the central costa and some of the lateral primary 
nerves more or less heset, now on the upper, now on the lower surface and now 
on both with hairs, bristles or spinules; the presence or absence or varied situation 
of these supply easy though not always reliable differential characters. In C. ciliaris 
and in other species of the same group the secondary and tertiary nerves are also 
covered with hairs, and if these nerves be numerous and very close together, 
the surface has the appearance of being uniformly hairy, as for example. in 
C. hispidulus. 
In a very few species a solitary spine is found, though not constantly, on the 
upper surface of the central costa near the base of the leaflet (C. tenuis and C. Rotang). 
In C. spinifolius the leaflets are armed with 3-5 erect and comparatively strong true 
spines. The leaflets of C. salicifolius are also more or less supplied with a few spines 
of this character; these, however, are absent from its vam. leiophyllus. 
In texture the leaflets of Calamus are usually thinish, sometimes sub-herbaceous 
or membranous, often chartaceous, and occasionally thinly coriaceous; very 
frequently both surfaces are of the same green colour, but the upper adMaed da 
most usually shining while the lower is dull. In comparatively few species the 
lower surface is more or less conspicuously different in colour, being mealy-puly- 
erulent and subpurpurescent in C. Grifithii, glaucescent in C. cæsius, mealy-ochraceous 
in C. symphysipus, mealy-white in C. arborescens and C. hypoleucus, or decidedly 
white and as if coated with a thin chalky layer in C,  Lobbianus, C. leucotes and 
C. discolor. Only in €. deerratus have I observed the lower surface sprinkled with 
small punctiform scales. | 
The margins of the leaflets of Calamë are very seldom absolutely smooth; most 
commonly they are furnished with cilia or very small adpressed or spreading 
spinules. 
The leaves of Calami usually retain their light green colour in dried specimens, 
but certain species, especially those of the C. andamanicus and of the C. platyspathus 
groups, assume in drying a light brown or tobacco colour, while ©. spathulatus, 
C. Martianus, C. insignis and a few others are readily recognisable in herbarium 
specimens by their bright yellow hue, : 
V.—The Leaf-Sheaths. 
The leaf-sheaths of the leaves of Calamus are very important organs of the 
plant. In most Calami, in all those species we may say that are scandent, a leaf- 
sheath arises from each ring of the stem and forms a complete more or less elongated 
cylindric tube round the internode immediately above. In the non-scandent species 
the leaf-sheaths are more or less open along the ventral aspect. | : 
The leaf-sheaths are always of a firm, tough or more or less coriaceous texture, 
and are sometimes even woody; but their leading characteristic is that they are 
always more or less covered with spines, which assume a great variety of forms and 
furnish one of the most conspicuous and useful diagnostic characters ise this Gee 
nation of many species. "Eg vimecs 
