1904 | WYLIE: ELODEA CANADENSIS 3 
The apex of the receptacle now flattens and broadens slightly, 
and, with the earliest indication of the floral parts, a cylindrical 
mass of tissue grows up (figs. 5-0), leaving a triradiate slit 
down its center, the walls being closely pressed together. The 
various parts of the flower continue meanwhile to develop at the 
outer end of this rapidly elongating growth. The calyx pushes 
out first (fig. 5), the sepals soon curving over the growing parts 
within; next comes the whorl of three sterile stamens (jigs. 8-9), 
followed by the three stigmas (jigs. ro—r2) ; last of all appears 
the corolla (figs. rz—72). 
Simultaneous with the development of the stigmas at the 
outer end of this floral tube is the growth of the ovules within 
its base. These push out from the surfaces of the central open- 
ing (fig. 10), but it is only as they develop that traces of the 
ovarian cavity appear (fig. zz). The walls which have previously 
‘remained in contact are now pushed apart, forming the rounded 
triangular ovary (fig. 72). The parts above ultimately coalesce, 
roofing over the cavity. 
The various parts of the flower having been established, the 
floral tube, that region of fused parts between ovary and sepals, 
enters upon a period of more rapid elongation. The direction 
of growth is at first a negative geotropic response, and the young 
flowers stand up quite stiffly, but during later development proper 
orientation is probably due entirely to the buoyancy of the 
enclosed gases. Very early in the history of the flower the begin- 
nings of three rows of air spaces can be seen, extending through 
its whole length (fg. zz). These start as rifts between cells and 
increase in size with the growth of the flower (fig. 72), until at 
maturity they constitute a large part of its volume. It is the 
low specific gravity of the floral tube that insures its direction 
toward the surface of the water, as these parts are very weak 
and cannot support themselves. A cross-section of the floral 
tube shows an outer ring, composed of two layers of cells, and 
a central conducting strand joined to the outer part by three 
bridges of tissue, leaving the three rows of air spaces between. 
The outer wall has no stored food, but all other cells are richly 
provided with starch. 
