1912] STEVENS—SEED OF BUCKWHEAT 61 
Growth and nuclear division are most rapid in the upper por- 
tion of the endosperm, that is, in the region between the growing 
embryo and the degenerating nucellar tissue. Cell formation 
begins in this region about the time the cotyledons first appear in 
the embryo. The cells arise centripetally and with great regu- 
larity. Apparently only a single nucleus is included in each cell, 
and there is no evidence of nuclear fusions. Cell formation gradu- 
ally extends both above and below the region where it originates, 
and soon a marked differentiation is evident in the endosperm. 
At the stage shown in fig. 2, cell formation has progressed till a 
portion of the endosperm, some 8 or to cells thick, extends entirely 
across, just below the embryo. Above, around the developing 
embryo, the endosperm consists of only a single layer of cells; 
while below the thickest region, the endosperm becomes thinner, 
consisting toward the bottom of fewer and fewer layers of cells; till 
at the base, for at least a third of its length, the endosperm does not 
become divided into cells at all, but consists merely of a layer of 
cytoplasm with scattered nuclei, enclosing a large sap cavity. 
This marked differentiation of the endosperm into two regions, 
one of which shows no cell formation whatever, suggested the 
chambered embryo sacs described by HOFMEISTER (5, p. 185), 
STRASBURGER (II, p. 111), and others, in which the first division 
of the primary endosperm nucleus is followed by the formation 
of a cross wall, dividing the embryo sac into two chambers, in only 
one of which the endosperm is developed. Careful study of early 
stages makes it seem certain, however, that no such cross wall 
occurs in the embryo sac of the buckwheat. 
Soon after the stage just described, a secondary differentiation 
becomes evident in the cellular portion of the endosperm; the outer 
layer taking on the appearance and function of a cambium layer, 
which cuts off cells only on the inner side. A similar condition 
has been figured by CHAMBERLAIN (2, p. 344) in the developing 
endosperm of Dioon edule. These “‘cambium”’ cells divide rapidly; 
and the continued growth of the cells thus formed forces the wall 
of the ovary outward, and causes the more central portion of the 
endosperm to extend downward toward the base of the ovule. 
No further development occurs in the lower portion of the original 
