the Monocotyledonous Leaf, 
497 
III. Summary, 
i. External Morphology. 
The first part of the present paper opens with a discussion and amplifi¬ 
cation of de Candolle’s theory of the Monocotyledonous leaf and of 
Henslow’s corollary to that theory. According to de Candolle’s theory, the 
typical Monocotyledonous leaf is interpreted as equivalent to the leaf-base 
and petiole alone of a Dicotyledon, but the present writer regards certain 
Monocotyledonous leaves as having been still further reduced until they are 
equivalent to leaf-bases only. Henslow’s corollary explains the ‘ lamina ’ 
of those Monocotyledonous leaves, which show a distinction between 
petiole and blade, as being merely an expansion of the apical region of the 
original phyllode and thus not homologous with the lamina of Dicotyledon ; 
the present writer proposes to call such a blade a ‘ pseudo-lamina ’ (p. 470). 
It is pointed out that these theories explain the venation of Monocotyle¬ 
donous leaves (p. 467). 
It is shown that the phyllode theory is in no way inconsistent with 
Miss Sargant’s hypothesis of the geophytic nature of the original Monoco¬ 
tyledonous stock. As regards the embryo, the present writer proposes the 
further corollary that the single cotyledon of the Monocotyledon is equiva¬ 
lent only to the fused bases and petioles of the Dicotyledonous seed-leaves, 
the cotyledonary laminae being unrepresented (p. 468). 
Asa Gray’s tentative suggestion that some Gymnosperm leaves might 
be equivalent to petioles is recalled and expanded, and the writer suggests 
its special application to the case of the Gnetales. It is pointed out that on 
the phyllode theory the Coniferae would be regarded as microphyllous by 
reduction (p. 472). 
2. Anatomy. 
The phyllode theory has hitherto been based entirely on external 
morphology, but, in the second part of this paper (p. 473), reason is given— 
on the ground of a comparison of Dicotyledonous scale-leaves, petioles, and 
phyllodes with the leaves of Monocotyledons—for the view that the occur¬ 
rence of inverted vascular bundles, towards the adaxial face of a leaf, may be 
an indication of phyllodic morphology. A list is added of the cases of such 
structure in Monocotyledons (pp. 478-81). In most of the cases to which 
this list relates, the facts of the anatomy were already known, but no one 
hitherto appears to have regarded the occurrence of these inverted bundles 
as furnishing—in correlation with the external form—the key to the mor¬ 
phological interpretation of the Monocotyledonous leaf. 
The isobilateral equitant leaf of Iris, &c., is regarded by the present writer, 
not as exhibiting congenital concrescence of the two halves of the organ, but 
