10 
lets given out at the junction of the tap-root and hypocoty] are fol- 
lowed by many similar ones from all parts of the primary root. 
The hypocotyl sometimes attains a length of two inches, but not 
often more than that. The cotyledons are at length borne on peti- 
oles as long as their blades. The first pair of leaves are obtuse, 
sometimes trifid, but more often only toothed. Sometimes one of 
the first pair of leaves will be trifid, the other not. The succeeding 
leaves are of the same nature as those of the mature plants. The 
leaves show a gradation from the rounded apex of the cotyledons 
to the acuminate final leaves. The plant is an annual. 
Ambrosia artemisefolia,L. The seeds and seedlings of this species 
differ from A. trifida, L, principally in size. The cotyledons, 
hypocotyl and root are less than one-half as large as the same 
parts in the larger plant. Another difference of much import- 
ance in determining the character of the plant, is the presence 
of buds in the axils of the lower leaves and cotyledons, and 
their early development into branches. Thus, early, is the 
diffuse nature of the plant determined. The buds of the lower 
axils, moreover, must be one of the characters by which the 
plant maintains its reputation as a persistent weed. The first 
pair of leaves are “trifid” or not; sometimes one is “ trifid,” 
the other not. The lobes of the leaves in A. artemis@folia are 
more rounded than in A. ¢rifida from the very first. 
NXanthium Canadense, Mill. (Plate CXXXV. H-M.) There are two 
akenes contained within the bur-like involucre of each pistillate 
head. The akenes are plano-convex, the plane side toward the 
axis of the head. They are black, elliptical, and tipped with 
the long protruding, but withered style. The cotyledons of the 
embryo are slightly dissimilar, the one on the convex or outer 
side being somewhat thicker than the other. The hypocotyl 
is very short, not more than one-sixth the length of the coty- 
ledons. 
The seedling emerges from the bur in the same manner as the 
seedling of Amérosia. Both akenes in a single head frequently 
germinate, usually not at the same time, however, so the seedlings 
will be at two stages of growth. The hypocotyl lengthens consid- 
erably. The conspicuous tap-root gives off numerous branches. 
The cotyledons are lanceolate, obtuse, somewhat narrowed at the — 
° 
