1914] PFEIFFER—THISMIA AMERICANA 129 
nor is there a ring of sclerenchyma about the vascular cylinder 
as reported for some other burmanniaceous forms. As might be 
expected, no stomata were found; the corollary of no air spaces 
follows logically. 
The floral axes appear to arise a short distance back of the tip 
of the root (figs. 4,20). The first external evidence of their develop- 
ment is a single small excrescence (fig. 20a). Later two growing 
points, usually point upward, are distinguishable. Growth is 
guite rapid and soon results in a first root and a floral axis 
(fig. 20), from the base of which other roots take origin (figs. 
21, 22). 
In prepared material, the earliest stage in the development of 
the bud is shown in fig. 12. A region of rapidly dividing cells occurs 
below the epidermis in a somewhat arched mass. At this stage the 
main root itself is in such an undifferentiated condition that the 
endodermis and neighboring tissues are not yet distinct. In 
slightly older stages, a break is seen to occur between the cortical 
cells of the root and the growing cells of the endogenous branch, 
which now has a slightly lobed margin (fig. 13). At this time, the 
beginning of the first root to be developed may be seen (figs. 13, 19) 
as a mass of meristematic tissue to one side of the floral bud. By 
rapid growth the root overtakes the stem from which it originated, 
so that when the two structures have emerged a little beyond the 
boundary of the main root, they are about the same size (figs. 14, 
15). At this time the floral part is still protected by the arch of 
primary root cortical tissue, but the root tip soon breaks through 
the cortex, becoming much the longer organ (fig. 16). A renewed 
Srowth of the floral axis and the development of other secondary 
Toots from the main floral axis (fig. 17) finally result in a horizontal 
Position of the first root, which had previously stood erect beside 
the floral axis. 
In the development of the axis, the rudiments of the bract 
leaves appear laterally (fig. 17). After elongation and the develop- 
ment of the leaves, the differentiation of the floral parts occurs 
(fig. 18). The perianth tube develops early. At the same time, 
the stamens begin their development. The ovary with its ovules 
Is late in appearance, a case similar to that in Orchidaceae. When 
