DEVELOPMENT OF SEED IN POLYGONACEAE 
473 
parently carries food material from the chalazal region to the develop- 
ing endosperm. The remaining nucellar tissue becomes broken down 
comparatively early. 
In Polygonum, Rumex, and Rheum, the cellular endosperm appears 
first in the micropylar region, while in Polygonella it appears uniformly 
about the periphery of the embryo sac. The cellular endosperm in- 
creases in extent by the activity of a cambium-like layer differentiated 
very soon after cell formation appears. Some time before maturity 
of the seed this cambium" layer ceases cutting off cells and becomes 
differentiated into an aleurone-containing layer, which, in Polygonum, 
Rumex, and Polygonella, through further tangential cell division, be- 
comes several cells thick in the micropylar region. 
In Polygonum, Rumex, and Rheum, the suspensor is from two to 
four cells in length, while in Polygonella it is about twelve cells in 
length, the portion next to the embryo consisting of two rows of cells. 
The embryo in its development to maturity comes to occupy a 
position either in the axis of the seed, an angle of the seed, or against 
one of the faces of the seed. The first position is seen in Fagopyrum 
esculentum and Rheum Rhaponticum; the second in Polygonum Persi- 
caria, P. Convolvulus, P. sagittatum, P. aviculare, P. tenue, and Poly- 
gonella articulata; the third in Rumex crispus and R. acetosella. Only 
in Polygonum, Fagopyrum, and Rheum is the position of the embryo a 
fixed character. 
The germination of Rumex crispus, Fagopyrum esculentum, Poly- 
gonella articulata and Polygonum scandens, shows that the aleurone 
layer has presumably a digestive function, secreting a ferment which 
converts the insoluble starch of the endosperm into a form available 
for the germinating embryo. The cells of the layer become much 
enlarged, and their cytoplasm finely alveolar and granular. In 
Rumex, Polygonella, and Polygonum chis increase in size of the aleurone 
layer causes the micropylar portion to appear outside the seed coats. 
In Rumex and Fagopyrum, the absorbed carbohydrate is tem- 
porarily converted back into starch in the tissues of the germinating 
embryo, the cotyledons being the principal storage region. 
Yale University 
