for a considerable time without being injured and are borne about by currents. Shores of streams and islands receive many of their plant seeds in this way. The cocoanut palm is a notable seed of this kind and is found widely scattered over tropical islands.
97.Seeds and their Germination.
Experiment 104. -Take two common dinner plates and place in the bottom of one of them two or three layers of blotting paper and thoroughly wet it. Place some wheat or other kinds of seeds upon this. Now invert the other plate over the first, being careful to have the edges touch evenly. This makes a moist chamber and gives the most favorable conditions for germination. Do all the seeds germinate at the same time? Does the position of the seed make any difference? What takes place first in the process of germination? What appears first, the leaf or the root? Why does the seed shrivel up?
Experiment 105. -Cut open several seeds, such as pumpkin, squash, bean, corn, and drop on to the inside of each a few drops of the iodine solution made in Experiment 100. Do the seeds show the presence of starch?
Experiment 106. -Soak some beans for about twenty-four hours. Rub off the skin from two or three and examine their different parts carefully. Plantthe beans in a box of damp sawdust. Put the box in a warm place. Plant some corn that has been soaked for two or three days in the same box. After the seeds have been planted several days, carefully remove a bean and a grain of corn and examine. Make a sketch of each of the seeds.
After a few days more remove another seed of each and examine and sketch. Continue to do this until the little plants have become quite well grown. Do the two seeds develop alike? Which of the seeds has two similar parts? These two parts are called cotyledons. What appears to be the use of these parts to the sprout? Consult the results of Experiment 104. Note the root development in each seed and the stem development. The sprouts get their food from the seed.
Fig. 102.
When we examined the different seeds in Experiment 105, we found that they each contained starch. When the seeds were soaked and planted, we found that a part of the seeds began to grow, forming a sprout. This part is the embryo already described. We also saw that the bean seed divided into two like parts which gradually withered and shrank, as the sprout grew, while the corn had only one such part.
These parts are called cotyledons, or seed leaves(Fig. 102). The bean seed is a dicotyledon (two seed leaves) and the corn a monocotyledon (one seedleaf). These cotyledons are the food storehouses for the germinating seed. As the sprout grew, the root, with its root hairs, developed, and the stem with its leaves. When these had grown strong enough, the cotyledons, having performed their part, dropped off. The plant was now ready to prepare its own food by the aid of the sunlight.
Experiment 107. -Place several beans in a tumbler of damp sawdust and put it in a warm, light place. Keep the sawdust moistened. After the beans are well sprouted, with a sharp knife cut one of the half beans or cotyledons off from a sprout. Cut both cotyledons off another sprout. Put the sprouts back on the sawdust. Do the sprouts grow as well as those of the other beans?
Experiment 108. -Fill a 16-ounce wide-mouth bottle about one third full of peas or beans. Pour in water enough to more than cover them. Tightly cork the bottle and put in a warm sunny place. Put another similar corked empty bottle beside it. Allow the bottles to stand for several days until the peas have sprouted. Remove the cork from the bottle containing the peas and insert a burning splinter. Do the same to the empty bottle. Why does not the splinter burn as well in each? If on being placed in either bottle the splinter is smothered out, it shows the presence of carbon dioxide.
Experiment 109. -Fill two 8-ounce wide-mouth bottles each about one third full of coarse sawdust and fill the remaining part with peas which have been soaked for a day. Pour in sufficient water to cover the sawdust. Cork one of the bottles tightly, leaving the other open. Put the two bottles in a warm sunny place. Whenever necessary, pour on sufficient water to keep the sawdust in the open bottle wet. In which bottle do the seeds sprout the better? Does air appear to be necessary for the growth of seeds? As determined by the previous experiment, what part of the air is used?
We found in Experiment 107 that if the cotyledons were cut off before the sprout had become sufficiently mature, it could not continue its growth. In Experiment 108 we found that the sprouting seeds took up oxygen from the air and gave out carbon dioxide just as animals do. Energy was needed and this energy was obtained by combining the carbon in the seed with the oxygen in the air, as it is when wood is burned. We found in Experiment 109 that the seeds could not sprout well unless sufficient air was supplied. That was because there was not enough oxygen supplied to furnish the necessary energy.
Experiment 110. -Place several sprouted seeds in each of two tumblers nearly filled with damp sawdust. Put these tumblers side by side in a warm light place. Cover one of the tumblers with a box painted black so as to exclude the light. In which do the seeds grow the better?
After the seeds were sprouted and had begun to prepare their own food, it was found in Experiment 110 that they were not able to do this unless exposed to the light of the sun. The parent plant had stored, in alatent form in the seed, energy which it had received from the sun. This potential energy the sprout was able to change into the kinetic form by the aid of oxygen, and to use in the work of growing. After this latent energy had been expended, it had to fall back upon the direct energy of the sun which came to it in the form of sunlight.
98.Fungi.
Experiment 111. -Expose a piece of moist bread to the air for a short time and then put it into a covered dish so as to retain the moisture. Does any change take place in the bread? Examine with a magnifying glass the mold which appears.