1918] PFEIFFER—THISMIA 350 
sacs would naturally drop to the floor of the cavity, that is, the 
roof of the ovary. In this fall it is obvious that the grains cannot 
come in contact with the stigma, which is separated by the stamen 
tube, although grains have been observed along the style. The 
cells of the inner surface of the stamen tube are often glandular 
in nature (fig. 16), although this would seem to have no special. 
significance except in connection with the entrance of insects. It 
seems likely that the latter are necessary agents in pollination 
because of the mechanics involved. 
The placentae which appear in the ovary during the development 
of the microsporangia give rise after a time to the primordia of the 
ovules (fig. 1). The surface of the placentae first becomes uneven 
through the appearance of the little lobes marking the rudiments. 
Soon the inner integument appears, and finally, as the ovule assumes 
the anatropous orientation, the outer integument is quite distinct 
except on the side where the funiculus appears. Meanwhile the 
hypodermal archesporial cell has become differentiated (fig. 2). 
The condition of mother cells usually occurs in the stamens at the 
same time that this archesporium appears in the ovule (cf. figs. 2 
and 15). This cell represents the megaspore mother cell directly, 
since no parietal cells are developed here. It enlarges noticeably, 
and at length undergoes nuclear division, during which the chro- 
matic material becomes massed at one side of the nucleus in synap- 
sis (fig. 2). After division two cells separated by a thin wall are 
evident (fig. 3). At the same time the whole ovule is developing 
rapidly, as shown by the spindles in the tissue about the megaspore 
mother cell or its progeny. The two daughter cells divide further. 
The spindle in the outermost cell is oriented at right angles to the 
long axis of the ovule, that of the inner parallel to this axis. The 
result is that there is a pair of megaspores side by side which fre- 
quently are so crushed together in later stages that they lie obliquely 
(fig. 5) or appear finally as one (fig. 10). Sooner or later these cells 
disorganize, as does the sister cell of the functional megaspore, 
which lies innermost in the series of four. The pressure of develop- 
ment usually shows first on the outermost megaspores (fig. 5), 
but sometimes the third non-functional one is crushed first 
(fig. 6). 
