certain Monocotyledonous Leaves. 333 
interpretation of the arrow-head c lamina ’ which I have suggested in a 
former paper. 1 In Fig. 2 G the upper part of the leaf-limb is reached. 
Fig. 2 D shows the detachment of the auricles by means of invaginations, 
indicated by arrows, and the same stage is also seen in Fig. 2 H, drawn 
from another leaf. 
HELOBIEAE — Hydrocharitaceae. 
w Hydrocharis. 
Microtome sections through the leaf-buds of Hydrocharis Morsus- 
ranae , L., show that the orbicular floating leaves are sheathing at the 
base (Fig. 4 a). The cordate basal lobes of the ‘ lamina ’ are cut through 
on either side and hence appear as detached objects (c. and c\). The 
sheath passes upwards into the paired stipules (st. and st'.), which are seen 
in Fig. 4 B in process of separation from the petiole. In Fig. 4 C the two 
stipules and the petiole (pet.) are entirely free from one another. Fig. 4 D 
shows the ‘ lamina ’ (/./.), which is produced by lateral expansion of the 
petiole. 
PRINCIPES— Palmae. 
I have considered the Palm-leaf in some detail in a previous paper , 2 
r and have shown that in this family the apparently plicate leaf-limb 
originates, not by folding — as has been generally supposed — but by means 
of a series of invaginations involving the petiolar tissues. So I shall now 
refer very briefly to two cases only. 
Areca . 
Figs. 5 A-E illustrate the passage from the sheath (Fig. 5 A) through 
the petiole (Fig. 5 b) to the ‘ lamjna ’ (Fig. 5 E) in Areca sapida , Soland. 
It will be seen that the plication arises by means of a series of dorsal and 
ventral invaginations penetrating between the main vascular strands (m.b., 
i. v /. 2 , /.* r v /'. 2 , /%), which can be followed from section to section. The 
process is a rapid one ; a distance of only 0-35 mm. intervenes between the 
first sign of the first invagination and the stage represented in Fig. 5 D. 
Oreodoxa. 
I add three drawings (Figs. 6 A-C) to illustrate the relations, in form and 
skeletal system, between the petiole and ‘ lamina ’ in a second case — 
Oreodoxa regia , H. B. et K. The bundles are lettered as in P"ig. 5. The 
first pair of invaginations, indicated by arrows, come into view in 
Fig. 6 B. 
SYNANTHAE— Cyclanth^ceae. 
Carludovica . 
Many years ago Eichler , 3 in his memoir on the developmental history 
of Palm-leaves, drew attention to their resemblance to those of the 
Cyclanthaceae — a comparison which has frequently been emphasized by 
1 Arber, A. ( 1921 2 ). 2 Arber, A. ( 1922 1 ). 3 Eichler, A. W. ( 1885 ). 
B b 
