THE SEED. 171 
we add to this characteristic some other considerations taken 
from their size, and the structure of their grains, we might detect 
the adulteration of flour by a simple microscopic o 
servation, and at a mere glance. 
The grains in Wheat (Fig. 268) are lenticular, ellip- 
tical, and egg-shaped. It is easy to distinguish these 
from the grains of the Potato (Fig. 269), which are 
generally larger, egg-shaped also, but with punctations, 
surrounded by certain zones, more or less regular and 
defined. In Maize (Fig. 270), the starchy granules of 
the horny part of the albumen are polyhedral, and 
nearly always show a punctation placed in their centre. 
In the Oat-plant, the starch grains are of several 
sorts. Some are simple, and their form is oanioatig Fie. 267—Sec- 
egg-shaped, and fusiform. Some are formed of tw 
three, four, or a higher, but still limited number a elements. 
There are some, also, compound, either eens or egg-shaped ; 
their diameter reaching about 
the five hundredth part of a 
millimetre, and their surface, 
under the microscope, resem- 
bling a mosaic of polyhedral 
segments. We find other sub- 
stances besides starch in the 7% 
thin-walled cells of the albumen “& ge 
of theCastor Oil-plant,and in the “9¢%& 
thick-walled cells of the albumen 
of the Date. Oily matter abounds 
there. They are filled with cor- 
puscles of a complex structure, 
whose chemical nature is not yet determined. These corpuscles, 
which in certain plants somewhat resemble grains of starch, 
may be termed mealy grains. They are more or less soluble 
in water, and are coloured yellow by iodine. Grains of starch 
are, on the contrary, insoluble in water, and are coloured blue 
by iodine. A very natural question here suggests itself as to 
the mode of transport and vitality of seeds; in short, as to the 
physiological phenomenon of germination. 
Fig. 268.—Starch Grains of Wheat. 
