460 Arber . — On the Leaf Structure of certain Liliaceae, 
Judging from the three species which I have examined, I am disposed 
to think that there is so sharp a difference in leaf morphology and anatomy 
between the Section Molium and the Alliums belonging to the preceding 
Sections that it is conceivable that Molium deserves elevation into 
a distinct genus, or even that it might be well to treat both A. ursimmi and 
A. Moly as generic types . 1 However this may be, it certainly seems that it 
is difficult to explain the leaves of this Section on the same lines as those of 
Sections I-IV. The most probable view appears to me to be that the - 
leaves of Allium Moly, A. Chamaemoly , and A. ursinum dp not, like the 
Figs. 32 and 33. Figs. 32A-D, Brodiaea congesta, Sm. (xylem, black; phloem, white; m.i.d. 
= main inverted bundle). Fig. 32 A, transverse section of limb of leaf ; pal. — palisade parenchyma 
(x 11). Fig. 32 B, transverse section of another leaf near apex (x 18). Fig. 32 c, transverse 
section close to extreme apex (x 18). Fig. 32 d, base of sheathing leaf and first foliage leaf ot 
young vegetative shoot (x 11). Fig. 33, Polygonum amphibium, L. Transverse section of petiole 
for comparison with limb of Brodiaea ; m.i.b. = main inverted bundle ( x 11). 
typical Alliums, consist of leaf-base and petiole, but are reduced to leaf-base 
alone, and that their ‘ laminae ’ are merely expansions of the upper part of 
this leaf-sheath. On this view the Molium Section would possess a more 
reduced and* advanced type of leaf than the rest of the genus. If this 
hypothesis holds good, we shall expect to find that the Alliums with the 
widest geographical distribution occur in other Sections, rather than in the 
Section Molium. This expectation is, as a matter of fact, realized, for no 
member of the Molium Section extends into the New World, whereas 
A. Schoenoprasum 2 and A. victorialis,vj\Xh their phyllodic leaves, occur not 
only in If urope and Asia, but also in North America. 
1 Irmisch, T. ( 1850 ), shows that A. ursinum differs markedly from A . Moly in its general 
morphology. 
2 In this connexion it may be mentioned that Lampa, E. ( 1900 ), has put forward the general 
view that in the Liliaceae the ‘ Rundblatt ’ is primitive. This writer does not allude to the 
possibility of interpreting the Monocotyledonous leaf in terms of the Phyllode Theory, but the 
