certain Monocotyledonous Leaves. 335 
a series of dorsal and ventral invaginations made their appearance in the 
sheathing region, and, penetrating between the bundles, produced a ‘ plicate’ 
form (Fig. 7 B). In the case of C. rotundifolia , H. Wendl, I was only able 
to obtain a much older leaf ; in this leaf there was a well-marked cylindrical 
petiole, in which the process of invagination took place. 
SpAthiflorae— A raceae. 
Calla . 
The leaves of Calla palustris , L., have a sheathing base enclosing the 
younger leaves (Fig. 8 A), continued upwards, on the ventral side, into 
a conspicuous stipula adnata (s.a.) (Fig. 8 B). When this stipule becomes 
free (Fig. 8 c), the petiole (pet.) assumes its definitive form. In Fig. 8 D 
we have reached a point above the top of the stipida adnata , and the 
two basal lobes of the cordate ‘ lamina J (c. and c.) are cut across at a 
level below their connexion with the petiole. Fig. 8 E shows the detach- 
ment of these lobes by a pair of invaginations. In Fig. 8 F we see the 
‘ lamina ’ arising by lateral winging of the petiole, while in Fig. 8 G it is 
completely formed. Figs. 8 H and I show its termination in a Solid apex 1 
in which all dorsiventrality is lost, and in which the bundles fuse into 
a vascular plexus. The solid tip of a younger leaf (f. 2 ) is shown in 
Fig. 8 c. 
Arum. 
The leaf-development in Arum italicum , Mill. (Figs. 9 A-F) closely 
recalls that just described for Calla. The auricles (a. and a'., Fig. 9 C) 
resemble the cordate lobes at the base of the ‘ blade ’ in Calla , and they are 
detached by means of similar invaginations (Fig. 9 D). The bundles which 
pass into the auricles are at this stage scarcely differentiated, and I have 
not been able to trace their origin with certainty. In Fig. 9 B the top of 
the sheath (j.) takes a form which recalls the stipida adnata of Calla , but 
this is perhaps an exceptional development, for in serial sections of two 
other young leaves, the sheath was found to pass uniformly into the petiole, 
without this ligulate appearance at the upper margin. 
Figs. 10 A-E represent the passage from sheath to apex in the first 
plumular leaf of Arum maculatum , L. This leaf is of the simple, non- 
auricled type, and there is a suggestion, in the transition from the petiole 
(Fig. 10 c) to the ‘ lamina ’ (Fig. 10 D), that invagination may play some 
part in the development of the latter.. 
Epipremnum. 
For comparison with Calla and Arum, I cut sections through a lateral 
bud of Epipremnum mirabile, Schott, and I found that the leaf in its early 
stages (Figs. 11 A-D) conforms to the same type -as in the two former 
genera. The detachment of the auricles (a. and a'., Figs. 11 A and B) and 
1 Arber, A. (1922 2 ). 
B b 2 
