DEVELOPMENT OF SEED IN POLYGONACEAE 
467 
tion forces the coat of the fruit apart at the apex, the break appearing 
at the angles of the fruit. As the embryo increases in size, the tip 
and then the whole radicle appears outside the fruit, as shown in 
figure 22. In so doing the micropylar portion of the shriveled testa, 
D', is either pushed aside or carried outside a short distance with the 
radicle, R. As the radicle increases in length, the increase in size of 
the aleurone cells mentioned above, causes the micropylar portion of 
the layer, L, to appear outside the fruit and clasp the radicle, thus 
preventing any of the dissolved food material escaping from the seed 
in its passage from the endosperm to the embryo. This collar-like 
structure must also prevent to a great extent the entrance of water 
from without, which would dilute this food material, or bacteria and 
fungi which would cause its destruction. 
As the radicle of the seedling continues to elongate it grows down- 
ward {fig. 23, R) and enters the soil, there becoming anchored by 
numerous root hairs and secondary roots. There occur at the same 
time, an elongation and broadening of the cotyledons, and a slight 
differentiation of the stalks. As germination continues the basal 
portion of the cotyledons emerges from the seed {fig. 24). By this 
time, the plumule which was hardly differentiated in the mature 
embryo, has attained a length of about 2 mm. and is cylindrical in 
form {fig. 24, P). The vascular system of the young seedling, which 
was undifferentiated in the mature embryo, has now become quite 
clearly differentiated. As the elongation of the cotyledons is occurring, 
the hypocotyl increases in length, raising the cotyledons with the 
seed adhering to the surface of the soil. At the stage shown in figure 
24 the starch has all been absorbed from the starchy endosperm except 
within the regions included by the dotted line. The depleted cells 
retain practically their normal shape, only being broken down as the 
cotyledons increase in size and press against them. The inactive 
aleurone cells have lost their contents and their walls have become 
collapsed. Very soon after this the broadening cotyledons, which 
have now developed chlorophyll push off the wasted remains of the 
seed and become erect. 
Fagopyrum esculentum 
As the writer has not included a representative of the genus 
Fagopyrum in the morphological discussion of the Polygonaceae, a 
description of the mature fruit of the buckwheat, F. esculentum, will 
be given at this time. 
