THE SEED AND GERMINATION 33 
the protein being legumin, a substance of similar 
composition to the protein which forms the curd of 
milk. The legumin is so plentiful that a drop of nitric 
acid placed on the inner side of the cotyledon produces 
an intense yellow. Now examine the young plant that 
lies curved between the cotyledons. Observe that it is 
attached to both cotyledons at about its middle point. 
The portion above the point of attachment is the 
plumule or young stem, and, by examining this with a 
lens, the undeveloped leaves may be seen. 
Immediately below the cotyledons is the hypocotyl, 
which in the broad bean never appreciably develops; 
but. which, in the searlet runner, pumpkin, and many 
other plants lengthens to such an extent as to lift the 
cotyledons well above the ground. In such eases the 
hypocotyl develops to form the lower part of the stem. 
Continuous with the hypocotyl, but showing no definite 
point of junction therewith, is the radicle, or young 
root. This points towards the micropyle, through 
which, under suitable conditions, it will, later on, 
emerge. | 
The cotyledons, plumule, hypocotyl, and radicle 
collectively form the embryo bean plant. 
The so-called sunflower seed (Figs. 16-18) is really 
a fruit, in which the seed is still covered by the original 
seed case which has been formed from the ovary wall. 
Take one of the soaked specimens and observe that 
the seed case may be split along the edge. If this is 
done carefully it will be seen that the enclosed seed 
is attached to the pointed end by a very short stalk. 
On removing the thin seed-coat, separate the two 
cotyledons and observe the small plumule and radicle 
situated at the extremity of the pointed end. The 
iodine test shows that starch is absent from the cotyle- 
dons, but the nitric acid and tissue paper tests show 
that proteins and oil are abundant. 
