364 BOTANICAL GAZETTE [NOVEMBER 
account for the poor set of seed in such cases, for insects working 
over the patch would not bring in so much viable pollen to the 
weak plants as if there was a commingling of the two. 
Development of seeds 
The fertilized ovule enlarges rapidly, mainly through the growth 
of the embryo sac. The sac destroys the nucellus except a crushed 
remnant at the bottom of the sac. The raphe and chalazal spur 
enlarge at the same time, and add to the bulk of the seed as a whole. 
The endosperm develops slowly, remaining for a considerable 
time as a layer lining the wall of the sac between the base and the 
suspensor at the tip. The embryo first develops a considerable 
mass of cells in the micropylar end of the sac, from the inner free 
surface of which the functional embryogenic cells are developed 
(CouLTER 7). This inner surface may become lobed, and then 
gives the condition called polyembryony by JEFFREY (13) and 
ScHAFFNER (20). Twin embryos developed in one case out of 
several hundred seeds germinated in this work; these were united 
near the upper end, but completely free below, and their vascular 
systems were distinct. These embryos probably were formed 
from two adjacent lobes from the free surface of the suspensor, 
becoming united through the incorporation of some cells in common 
from the base of the lobes. In pushing into the soil, the elongation 
had occurred in the zone just behind the stem apex, and this was 
distinct in each of the two embryos, producing the condition shown 
(fig. 36). 
The general conditions of the sac, endosperm, and suspensor 
in E. americanum are closely duplicated in Urtica cannabina, as 
studied by Mopmewsky (15). In both cases there is a thin 
lining of free endosperm nuclei along the walls of the sac, a con 
siderable suspensor at the tip, and a mass of deeply staining cells 
below the base of the sac. In Erythronium these cells form 4 
considerable mass, and extend backward to the termination of 
the raphal bundle at the chalaza. These cells stain deeply eve? 
in ripe seeds, and the adjacent cells of the remnant of the nucellus 
remain in close contact with the center of the base of the endosperm 
_in the ripe seed. This would indicate the purpose of these cells 
