FAMILIAR SEEDS, STRUCTURE AND GERMINATION 15 
The plumule is enclosed in the sheath of the cotyledon. 
In time it breaks through the sheath and bears leaves 
which come above ground. 
PRACTICAL EXERCISES. 
1. Make some iodine solution by dissolving 1 gramme of 
potassium iodide in 500 ¢c.c. of water and adding iodine until 
the solution is dark brown in colour. This solution stains 
starch blue and cellulose yellow. 
2. Soak a broad-bean seed in water for a few days. Then 
examine the external appearance. Note the testa, the hilum, 
and the micropyle. If the seed is squeezed a drop of water is 
pressed out through the micropyle. Make a sketch of the seed. 
Next remove the testa. Note the two fleshy cotyledons and the 
radicle, with its tip pointing to the micropyle. Split the seed, 
and note the plumule and radicle lying between the two coty- 
ledons, Draw a sketch showing these in position. Add a drop 
of iodine solution to the cotyledon. It turns blue, showing that 
starch is present in the cotyledons. 
3. Do the same with the seeds of castor oil, maize, mustard, 
sunflower, pine, pumpkin, onion and date plants. 
4, Place a few of each of the above seeds in damp sawdust 
(the mustard seed is best grown on damp flannel). As the 
seeds germinate make sketches of the different stages, showing 
the ruptured testa, the radicle emerging from the seed, the 
plumule, first leaves, and root branches. 
5, After the radicle has grown to about an inch in length, 
lay it alongside a rule divided into tenths of an inch and with 
a piece of thread dipped in Indian ink make marks on the 
radicle at every tenth of an inch. Now place it back in the 
damp sawdust. After a few days note which parts of the 
radicle have grown the most. 
6. Place about twenty pea seeds in a bottle containing a 
little water and closed with an air-tight stopper. Note that 
germination goes on for a little time and then stops. If the 
stopper be then removed and a lighted taper introduced, it 
is extinguished, showing that the oxygen has been used up. 
The seeds died because all the oxygen was used up and they 
