32 BOTANICAL GAZETTE [yuLy 
represents a transverse section of the awl-like limb of one of these 
peculiar American Sagittarias. For comparison, by its side is a 
transverse section of the petiole of the normal arrowhead leaf of 
S. sagittifolia L. It will be recognized at once that both in form 
and structure they are essentially identical, and it will probably 
be generally agreed that the leaf of S. teres is equivalent to the 
arrowhead leaf of S. sagittifolia, minus the blade. Domi (9) 
evidently takes this view, for he uses the term “‘Phyllodien”’ in 
describing these leaves. 
2. Leaves with a sheathing base and a flat ribbon-like limb.— 
These leaves are exceedingly common in the family, and are 
regarded as equivalent in morphological value to type 1, since in 
S. sagittifolia intermediate forms can be traced between thin 
ribbon leaves with a single row of bundles (fig. 3) and the almost 
radial petioles of the arrowhead type (fig. 2). For instance, 
among the transitional leaves between the juvenile ribbon and 
the mature arrowhead, a leaf was examined which was ribbon-like, 
but with a spathulate apex. It was found that the ribbon region 
was thicker than in the simple ribbon leaf, and, instead of having 
one series of bundles only, it had one small additional bundle 
above and one below the median bundle, and one below each of 
the main laterals, that above the median bundle being inverted. 
This showed an approach to the radial structure of the S. teres 
group. 
3. Leaves with a differentiated pseudo-lamina.—I have set forth 
elsewhere (1) the reasons for regarding the blade of such leaves as 
the arrowhead as “pseudo-laminae,”’ produced by the expansion of 
the distal part of the petiolar phyllode. How far the form and 
venation of the blades of the Alismaceae harmonize with this 
interpretation may now be considered. In some of the oval or 
cordate leaf forms there is little difficulty in seeing how the skeleton 
of the blade might be produced merely by the separation of the 
parallel petiolar veins, which at the apex return to their original 
approximation. This is the case, for instance, in Alisma parnassi- 
olium Bassi var. majus (fig. 6). A further development on the 
same lines has taken place in A. nymphaeifolium Griseb. (fig. 8), in 
which the veins v and 0’, curving into the basal lobes, give off second- 
