Notes . 
I2 5 
long considered probable that the terete leaf was in reality a connate 
pair, but the structure shows a single bundle, and therefore a single 
leaf/ 
As it happens that the tree in question often does produce some of 
its leaves in pairs the probability mentioned by Engelmann did not 
seem remote, and Sir Joseph Hooker 1 adopted this view, saying that 
£ the anomaly in the foliage is due to the cohesion of the two semiterete 
leaves of each sheath by their adjacent faces, and is far from being a 
constant character. In the plants at Kew the two leaves are as often 
free as connate ; and, on making a transverse section of any connate 
pair, it will be seen that the vascular bundle traversing the centre of 
the cylinder is, in fact, double, and that the two parts are sometimes 
separate/ 
In the hope of reconciling the discrepancies between these state- 
ments, or of ascertaining which is the more correct, I have recently 
repeated some observations, which I made first in 1883, both as to 
the minute anatomy of these leaves and as to their mode of develop- 
ment. These observations are so readily checked, that it will be easy 
to confute or to confirm the conclusions at which I have arrived. 
Alluding in the first place to the anatomy of the single cylindrical 
leaf, a transverse section through the middle shows that it is really, 
what it seems to be, a single leaf. The section is circular, the epiderm 
broken by stomata and consisting of more or less cubical cells, beneath 
which lies a double layer of thick-walled hypoderm. Close to the hypo- 
derm and each surrounded by a girdle springing from it are the resin 
canals, two or three in number. Then comes the leaf-substance of 
several layers of polygonal cells filled with chlorophyll and with 
abundant starch grains. The outermost of these cells have sinuous 
walls, while the innermost are straight-walled and radiate in all 
directions from the bundle-sheath or endoderm. This latter sheath 
consists of a circle of ellipsoidal colourless cells filled with starch and 
surrounding the circular (in section) pericycle. The pericycle con- 
sists of ordinary colourless parenchymatous tissue, interspersed among 
which are some relatively very large libriform cells, while in the 
centre is the vascular bundle proper, in the form of a wide crescentic 
band, the convexity of which is directed towards the axis, the con- 
cavity in the opposite direction. The thick-walled xylem occupies the 
side nearest to the axis, the thin-walled, but relatively more abundant 
1 Gard. Chron. 1886, July 31, p. 136. 
