456 
EDWARD F. WOODCOCK 
It was at the suggestion of Prof. A. W. Evans that this work was 
carried on, and it is to him that the writer is indebted for valuable 
assistance in all parts of the work, and to Dr. G. E. Nichols for liberal 
aid in the preparation of material. 
Description and Discussion of the Morphology of the Seed 
The growth and differentiation which take place in the ovules in 
response to the stimulus of sexual union have been studied in detail 
in the seeds of representative species in each of the genera Polygonum, 
Rumex, Polygonella, and Rheum, special emphasis being laid upon the 
morphology of the structures present in the mature seed. 
Polygonum 
P. Persicaria, P. aviculare, P. tenue, P. sagittatum, and P. Con- 
volvulus were studied in detail, but as there was a marked similarity 
in their development it will be sufficient to describe in detail only one 
species, e. g., P. Persicaria. The points of difference between this 
type and the remaining species mentioned will be taken into con- 
sideration. 
The early development of the embryo in P. Persicaria up to the 
stage at which the cotyledons begin to be differentiated appears to 
correspond almost cell for cell with the typical Capsella embryo. The 
suspensor of P. Persicaria, however, consists of only two or three cells, 
whereas in Capsella it is made up of seven or eight cells. 
Very soon after fertilization, free nuclear division begins in the 
embryo sac, and when the embryo has reached the octant stage, shown 
in figure i, the cytoplasm of the endosperm containing about 30 free 
nuclei forms a granular layer, EN, lining the embryo sac, K. A 
single outermost layer of the nucellus, N, extending to the micropyle, 
differs markedly from the rest. At some period before fertilization 
occurs, this layer becomes differentiated and is made up of closely 
packed, prismatic cells, characterized by rather dense granular contents 
and an absence of vacuoles. The embryo sac, occupying a central 
position in the nucellar tissue extends nearly to the base. The micro- 
pylar portion of the sac is expanded being separated from the inner 
integument only by the differentiated nucellar layer. 
As development proceeds growth and nuclear division occur most 
rapidly in the micropylar portion of the endosperm, in the region 
