16 INTRODUCTORY ESSAY. 
In C. erectus the ocrea is exceptionally large; it is tubular and entire while still 
enclosed in the terminal unexpanded shoot, but afterwards it is split along the ventral 
side into two halves, one on each side of the petiole, resembling two large auricles 
which are as much as 7 cm. in length, chartaceous and densely clad with hispid 
hairs. ! 
A small group of species from New Guinea have a still more striking form 
of ocrea resembling that of some species of .Kor/halsia ; in fact the ocrea of 
€. macrochlamys and C. ralumensis attain the extraordinary length of 30-35 cm, and 
are firm and thin in texture or chartaceous, elongate-conical or almost the shape of 
asses’ ears, in other cases the ocrea is at first membranous and tightly embraces the 
sheath above its own and ultimately becomes disintegrated into filaments or fibres. 
I do not know any Calamus in which the ocrea is transferred into a receptacle 
for harbouring ants, as is the case in some species of Korthalsia. 
VIII.—The Petiole. 
As we have already seen, the basal portion of the rachis of the leaf which 
does not bear leaflets is treated as the petiole. In Calamus therefore the petiole 
begins at the mouth of the sheath and terminates at the point of attachment of the 
first leaflets. The petiole is usually rounded or convex beneath and flat or chan- 
nelled above; it is frequently armed with prickles, usually longer along the margins 
than elsewhere. The petiole of the radical leaves and of the young plants is gener- 
ally a good deal longer and more cylindric than that of the adult plant, and in 
these the petiole of the upper leaves is shorter than that of the lower ones. 
IX.—The Rachis. 
The rachis represents the backbone or axis of the leaves in Calami just as in 
other Palms, and bears, right and left, a number of leaflets varying according to 
the species. In the description of the species the term rachis is applied only to 
that part of the axis of the leaves which bears leaflets, it having been decided to 
term the basal naked portion of the leaf-axis the petiole and the prolongation : 
ihe axis beyond the distal leaflets, when this occurs, the Cirrus. 
The rachis is not uniform throughout its length; being a continuation of the 
petiole it is more or less convex beneath towards the base and flattish towards the 
apex, where in all scandent species it is more or less armed with hooked prickles or 
claws; these are usually solitary lower down and become binate and then ternate 
towards the apex, and at last in some cases among the cirriferous species even 
quinate and ,half-whorled and of increased size and strength where the rachis begins 
to assume the essential features of a cirrus, 
On the upper surface immediately above the petiole, the rachis is usually very 
slightly channelled or almost flat, and shows on each side of the central part a 
longitudinal furrow within which the leaflets are inserted; higher up the two furrows 
gradually vanish, the central part becomes narrower and is transformed into a 
salient angle with two converging sides or facets. There, consequently, the rachis 
is triangular in section, bi-facetted with a salient angle above and flattish beneath. 
This shape is almost invariably assumed by the rachis from the middle onward to the apox, 
