LEAF STRUCTURE AND DEVELOPMENT 33 
LEAF STRUCTURE AND DEVELOPMENT 
The seedling leaves of A. triphyllum are simple, cordate to ovate 
abruptly acute, with a slightly cordate base. The blades are from 
5 mm. wide by 10 mm. long to 20 mm. wide by 30 mm. long. 
The venation is reticulate, pinnate, with two prominent basal 
branches ‘foreshadowing distinctly the plan of the mature tri- 
foliolate leaf ”’ (22, p. 48). The margin is very finely toothed. Itis 
slightly membranaceous and crisped. The upper surface is gla- 
brous, shining at first but becoming dull with age. The lower sur- 
face is distinctly glaucous after the leaf is fully expanded. The peti- 
ole may vary from 4-20 cm. in length. Its enlarged, hollow base 
covers almost entirely the new terminal bud of the corm. PLATE 
4, FIG. 58, shows a small group of average seedlings. 
The primordium of the first leaf is laid down some time before 
the seed is matured, and in the mature embryo the regions of 
petiole, midvein and lamina are clearly marked (TEXT FIGS. 21, 
22). During germination the 
blade develops rapidly, and, 
closely rolled, is pulled from 
the soil by the lengthening 
of the petiole, which usually 
arches in its escape from the 
ling leaf blade from its first 
appearance to its final expan- 
Wea An a ge ata sion. Occasional lobed leaves 
form and venation. XI. 
suggestive of the later com- 
pound leaves are found. Such 
a form with two lateral lobes symmetrically placed is shown in 
PLATE 3, FIG. 43. 
The leaf of the second year is typically trifoliolate (TEXT FIG. 36) 
and in all but size is like that of the mature plant. The leaflets 
are ovate to cordate, sessile, with acute apex and cordate to slightly 
tapering base. The lateral leaflets are slightly larger and less 
symmetrical than the terminal. They are pinnately net-veined 
with surface and margin as in both younger and older leaves. 
The leaves range in size from 3.5 cm. wide by 2 cm. long to 8 
