90.Plants and Animals. -Plants and animals are combinations of the earth"s elements endowed with life. By means of the sun"s energy they are able, the plants directly and the animals indirectly, to do both internal and external work which re- sults in growth, reproduction and other activities. Since plants and animals are entirely dependent upon the earth and sun for their existence, they, like other earth and sun phenomena, should be studied in this course.
91.Plants. -Although in their lower
microscopical forms it is very difficult to distinguish between plants and animals,THE GRIZZLY GIANT.
The monarch of all plants, 93 feet around at the base. Notice the cavalry at the foot.
yet the forms ordinarily seen differ greatly. Most plants are fixed and consist of root, stem and leaves, while most animals are movable and possess a variety of different parts. But some plants, like the seaweeds, appear to have no roots; some, like the dandelion, no plant stem, and some, like the cactus, no leaves.
If we dig around the base of a tree, we find in the soil a network of roots holding firmly erect a pillar-like stem with branches bearing a profusion of leaves. If we examine these divisions carefully, we shall find that each has a distinct part to play in the life work of the tree. We shall also find (1) that plants as well as animals need air, water andA TYPICAL PLANT.
Showing root, stem, leaf and flower.
other kinds of food, (2) that plants, like animals, take in, digest and assimilate food, and (3) that each in the higher forms has parts which are particularly adapted for doing these different kinds of work.
92.Plant Roots. -Plant roots not only usu-
ally secure the plant to the ground so that the stem may be supported, but they take up food from the soil and pass it on to the rest of the plant. In most plants all the foods except carbon and oxygen are taken in by the roots. The soil elements that the plants must have are nitrogen, potassium, calcium, magnesium, phosphorus, sulphur and iron. Water is composed of hydrogen and oxygen, while car- bon, the other necessary element, is taken from the air. The soil elements must be in soluble chemical combinations, such as nitrates, phosphates, sul- phates and so on.
Experiment 88. -Fill three 2-quart fruit jars each about half full of distilled water. Add to the water inthe first of these 1/2 gram of potassium nitrate, 1/4 gram iron phosphate,12/100 gram calcium sulphate and 12/100 gram magnesium sulphate. Add to the water in the second jar the same ingredients with the exception of the potassium nitrate. Replace this by potassium chloride. Put the three jars where they will receive plenty of sunlight and warmth and place in each a slip of Wandering Jew about 10 inches long. Note which slip grows the most thriftily. In the third jar there is no mineral food, in the first all of this food which is necessary and in the second all the necessary food except nitrogen.
In Experiment 88, it was found that in the distilled water the plant made but little growth. It did not thrive when the nitrogen was lacking, but grew very well when all the necessary elements were present. All plant foods must be in dilute solution before plants can appropriate them.
Experiment 89. -In another fruit jar make a strong solution of potassium nitrate or, as it is commonly called, saltpeter. Place in this a slip of Wandering Jew as was done in the previous experiment. Does the slip grow well? It has a great abundance of nitrogen, which was found so important. Place in a similar strong solution a growing beet or radish freshly removed from the ground. Notice how it shrivels up. Place a similar beet or radish in water. It is not similarly affected. What is the effect of strong solutions on plants?
If the solution is too strong, as seen in Experiment 89, the plant cannot use it. This is the reason many alkali soils will not support plants. The alkali salts are so readily soluble that the soil water becomes a solution stronger than the plants can use.
Experiment 90. -Place three or four thicknesses of colored blotting paper on the bottom of a beaker. Thoroughly wet the paper and scatter upon it several radish or other seeds. Cover the beaker with a piece of window glass and put in a warm place. Allow it to stand for several days, being sure to keep the blotting paper moist all the time. When the seeds have sprouted, examine the rootlets, with a magnifying glass or low power microscope, for the root hairs which look like fuzzy white threads. Touch the root hairs with the point of a pencil. They cannot, like the rest of the root, stand being disturbed. On what part of the root do the root hairs grow? As the blotting paper dries, what happens to the root hairs?
Plant roots are prepared particularly by the little root hairs, which were examined in Experiment 90, to take the film of water which surrounds the soil particles and carry this water to the stem and, through it, to the leaves. The water which the roots take from the soil is a dilute solution containing the plant food substances. Not only do roots absorb the water from the soil, but they secrete weak acids which aid in dissolving the mineral substances which the plants need. This can be seen where plant roots have grown in contact with polished surfaces, such as marble. These surfaces are found to be etched.
Experiment 91. -Cut a potato in two. Dig out one of the halves into the shape of a cup and scrape off the outside skin. Fill the potato cup about 2/3Fig. 83.
full of a strong solution of sugar. Mark the height of the sugar solution by sticking a pin into the inside of the cup. Place the cup in a dish of water. The water should stand a bit lower than the sugar solution in the potato cup. After the cup has stood in the water for some time, notice the change in the height of the denser sugar solution.
