382 REPORT OF THE HORTICULTURAL DEPARTMENT OF THE 
Extreme differences in specific gravity in the cases of cabbage 
seed and peas have been shown to be due to the presence of an 
unusual amount of air within the seed-coat; hence, strictly, the 
Specific gravity of the seed should not be spoken of as affecting 
its cultural properties. But wherever an unusual amount of air 
is found within a seed, other characters of the seed are found to 
be correlated with this condition so that indirectly the specific 
gravity of the seed is in a general way an index to, though not 
a measure of, the specific gravity of its essential parts. 
To ascertain whether differences in specific gravity obtain 
among the structural sub-divisions of the essential parts of the 
seed, examinations were made of squash seeds as material easy of 
manipulation. Squash seeds in their normal condition are uni- 
formly lighter than water. The outer seed-coats were removed 
from a number and the specific gravities of the kernels were 
found to range from 1.03 to 1.08. The radicles are much denser 
than the cotyledons as appears from the following dissections: 
Sp. gr. of cotyledons: 1.05 1.065 1.07 1.08 
tii: radieles): 1.105 1.12 L438 1.135 
The cotyledon lowest in density was accompanied by a radicle 
also lowest in density, and the cotyledon highest in density was 
accompanied by the radicle highest in density. It appears, then, 
that the densities of these two structural parts vary together in 
a general way, that is, apparently the development of these or- 
gans and the storage of reserve material within them proceeds 
together. This general statement is also supported by observa- 
tions on peas. 
The specific gravity of the two cotyledons is the same or prac- 
tically the same, both in the squash and in the pea, the only 
kind of seed on which observations have been made on this point 
by the writer. 
The cotyledons are of uniform density throughout, at least in 
the case of the squash, as may be shown as follows: If a single 
cotyledon be separated from its radicle and placed in a liquid 
of such density that it almost remains in suspension, the thinner 
distal edge comes to the surface first if the cotyledon rises, or 
remains longest buoyed up in the liquid if the thicker proximal 
end barely sinks to the bottom. But if the dark covering of 
the cotyledon be carefully removed all parts of it rise or sink 
