DEVELOPMENT OF SEED IN POLYGONACEAE 
469 
The first evidence of the action of the ferment is seen in the depletion 
of the starch in the micropylar and basal regions. The dissolved 
starch is apparently not used up as fast as it is absorbed by the embryo 
but rather a part of it becomes converted back into an insoluble form 
in the cells of the embryo as already noticed for Rumex crispus. 
The depletion of the endosperm in Fagopyrum proceeds much as in 
Rumex. 
As the starchy endosperm is being digested and absorbed by the 
embryo, the latter begins to increase in size. Very soon through the 
rent at the apex of the fruit the elongating hypocotyl and radicle 
appears outside the seed {fig. 25). The enlarged aleurone layer does 
not extend beyond the coat of the fruit as is the case in Rumex. 
In sections of the seed at the stage in which the radicle is just ap- 
pearing outside the seed, the elongated tannin sacs, mentioned by 
Solereder (17, p. 669) as occurring in species of Fagopyrum and Poly- 
gonum, are very evident. As further growth occurs these sacs increase 
markedly in length. Another interesting feature in the young radicle 
is the embryonic secondary roots which appear under the microscope 
as distinct slight elevations of the surface of the radicle. 
As these changes are taking place in the hypocotyl and radicle, 
the cotyledons are increasing quite markedly in width and length, 
and to a slight extent in thickness. This increase in proportions is 
doubtless due to cell divisions as well as increase in cell size. The 
petioles or stalks of the cotyledons, which are so short in the unger- 
minated seed that they can be hardly distinguished as such, take on a 
slow growth as germination continues. In the stage shown in figure 
25, they are only about .2 mm. in length. At about the fourth day 
of germination these stalks have become about i mm. in length 
and at their basal portion, merge into a swollen sheath-like structure 
of equal length {fig. 27, SH) which protects the developing plumule. 
As growth proceeds the basal portion of the cylindrical cavity of the 
sheath becomes lined in the region of the plumule with multicellular 
hair-like structures. The shape of the plumule {fig. 27, P) which is 
now about 4 mm. in length and almost fills the basal portion of the 
cavity, is that of an inverted top. 
At the stage just discussed which is shown in figure 27, the basal 
portion of the cotyledons are loosely folded about the hypocotyl, which 
has now increased quite markedly in diameter. The increase in width 
of the cotyledons causes them to become much more folded than orig- 
