THE SEED 15 
them cotyledons. Be careful not to break or displace the tiny 
bud packed away between the cotyledons, just above the 
hilum. Label the round portion of this bud, hypocotyl, and 
the upper, more expanded part, plumule. Which way does the 
base of the hypocotyl point; toward the micropyle, or away 
from it? Pick out this budlike body entire and sketch as it ap- 
pears under the lens. Open the plumule with a pin and exam- 
ine it with a lens; of what does it appear to consist? Do you 
find any endosperm around the cotyledons, as in the corn and 
oats? Break one of the soaked cotyledons, apply the proper 
tests (Exps. 2, 3, 5), and report what substances it contains. 
Where is the nourishment for the young plant stored? What 
part of the bean gives it its value as food? 
Notice that in the bean the embryo consists of three parts, 
the hypocotyl, plumule, and the two cotyledons, which com- 
pletely fill the seed coats, leaving no place for endosperm. 
Seeds like the bean, squash, and castor bean, which have 
two cotyledons, are said to be dicotyledonous. 
13. The castor bean.— Lay a castor bean on a sheet 
of paper before you with its flat side down; what does it 
look like? The resemblance may be increased by soaking 
the seed a few minutes, in order to swell the two little pro- 
tuberances at the small end. Can you think of any benefit 
a plant might derive from this curious resemblance of its seed 
to an insect ? 
Sketch the seed as it lies before you, labeling the pro- 
tuberance at the apex, caruncle. The caruncle is an append- 
age of the seed-covering developed by various plants; its use 
is not always clear. What appears to be its object in the 
castor bean? Refer to Exp. 13 and see if there is any other 
purpose it might serve. 
Turn the seed over and sketch the other side. Notice the 
colored line or stripe that runs from the large end to the car- 
uncle. This is the rhaphe, and shows the position that 
would be occupied by the seed stalk if it were present. Its 
starting point near the large end, which is marked in fresh 
