54 
S. L. Ghose 
Theoretical 
There are one or two points which seem to be of some theoretical 
interest in the anatomy of this abnormal leaf. In this example of 
enation the law of laminar inversion, according to which opposed 
laminar surfaces are similarly constituted, is obeyed in spite of the 
fact that the torsion of the “petiole” brings about some complication 
in the general arrangement of tissues. This law has been seen to hold 
good in nearly all the cases of enations mentioned by Worsdell (1915) 
and others. For comparison, sections were cut of a double-bladed 
leaf of Xanthosoma appendiculatum Schott, and I found that it 
obtained there also. Another interesting thing attracted my attention 
in some of the sections of the latter. Fig. 5 shows a transverse section 
of the leaf at the region of the base of the second blade. The “midrib” 
shows a number of invaginations all round, which seem to suggest 
a tendency to form more blades. The “petiole” shows no such in¬ 
vaginations. I cut a section of a normal leaf at a similar region and 
noted that it also showed these invaginations, though in a less marked 
degree. The genus Xanthosoma has already attracted attention on 
account of its tendency to produce leaf-enations. Worsdell (1915, 
2, p. 168) refers to the remarkable enations from the lower surface 
of its leaf. Velenovsky (1907, pp. 410-n) mentions the double- 
bladed leaf in X. atrovirens. Willis (1919, p. 692) mentions the pocket¬ 
forming habit in X. appendiculatum. Whether or not more than two 
blades are ever formed in X. appendiculatum I cannot say, but these 
invaginations seem to suggest that here a process of grooving, 
associated with development of wings, has been adopted for the for¬ 
mation of the “lamina,” as has been found to occur in the Palms 
and in some Irids by Arber (1921 and 1922). A series of sections 
through the abnormal leaf of X. appendiculatum shows this quite 
clearly. Just below the base of its second blade the “midrib” shows 
a number of ridges and invaginations all round the lower surface 
(Fig. 4). As we go higher up, one of these grooves situated near the 
middle of the lower surface becomes more marked, the epidermal 
cells round it become larger, the hypodermal cells slowly change into 
palisade parenchyma (Fig. 5), and the two ridges are finally trans¬ 
formed into wings, so that a second blade is produced. Thus it is clear 
that this second blade is produced as a result of grooving or invagina¬ 
tion, associated with development of wings. A little higher up, this 
groove closes, and the “midrib” has again only one blade, indicating 
that the second blade is only an elaboration of the two ridges pro- 
