1915] PLOW MAN—BOX ELDER 187 
fibrovascular strands, which become larger out to the first pair 
of leaflets. Beyond that point these strands are smaller, and they 
may be fewer. These medullary strands are larger and more 
numerous in petioles of leaves having the larger numbers of leaflets. 
In these cases the strands are often typically amphivasal, but 
with the greater part of the xylem directed upward. Large cells 
and ducts appear in the cortex, similar to those found in the cortex 
of the root. Neither A. saccharum nor A. platanoides (fig. 10) 
develops medullary strands in the petioles. In A. rubrum (fig. 8) 
there is a single small centrivasal strand, conspicuous for its dense 
and tanniniferous phloem. In A. saccharinum there are a few 
very small medullary strands clustered near a sclerotic rib that 
projects into the upper side of the medulla. In neither of these 
cases, however, is there any indication of a true amphivasal con- 
dition. The petiole of box elder is larger and less compact than 
that of the true maples. Sclerotic tissue is almost entirely wanting, 
and the same is true of crystallogenous and tanniniferous cells. 
All of the maples possess these three sorts of cells in greater or less 
amount. The petiole of A. rubrum is particularly dense (fig. 8). 
Anatomy of reproductive axis and fruit 
The reproductive axis of box elder is characteristically com- 
pressed, so that the cross-section is a broad ellipse, with axes 
about in the ratio of 3:4 (fig. 5). The surface is ribbed and the 
cuticle is very thick. The pith is composed of cells of very unequal 
size, some of them quite large. The xylem ring is interrupted 
by 10-15 one or two-seriate medullary rays. The hard bast is 
prominently developed in a thick continuous zone which is 
crowded close upon the phloem. All cell walls are comparatively 
thick. 
In A. platanoides (fig. 4), which is fairly typical of -the maples, 
the reproductive axis is quite cylindrical, smooth, and covered with 
a thin cuticle. The pith cells are uniformly rather small. The 
xylem ring is interrupted by 5-8 two to six-seriate rays. The hard 
bast zone is but slightly developed, narrow, widely interrupted, and 
remote from the young phloem. Compared with the vegetative 
stems, the reproductive axis of box elder and the maples shows an 
