Experiment 92. -Bore a 3/4-inch hole 3 or 4 inches deep in the top of a carrot. Scrape off the outside skin and bind several strips of cloth around to keep the carrot from splitting open. Fit the hole with a one-hole rubber stopper having a glass tube about 1 meter long extending through it. Fill the hole in the carrot with a strong sugar solution colored with a little eosin and strongly press and tie in the stopper. The sugar solution will be forced a short distance up the tube by the insertion of the stopper. Mark with a rubber band the height at which it stands. Submerge the carrot inwater and allow it to stand for a few hours. Mark occasionally the height of the column in the tube. Taste the water in which the carrot was submerged. There has been an interchange of liquids within and without the carrot.
The plant root takes up its water in the same way the water was taken into the sugar solution of the potato cup or of the carrot. The water or sap within the substance of the root is denser than the soil water, just as the sugar solution was denser than the water outside. It has been found that whenever two liquids or gases are separated by an animal or plant membrane, there is an interchange of the liquids or gases, the less dense liquid or gas passing through morerapidly. This is called osmosis and is of the greatestimportance to both plants and animals.
All animals and plants are made up of exceedingly minute parts, called cells. Fig. 84 shows the cells in a leaf and the leaf hairs greatly magnified. The higher plants and animals arecomposed of vast numbers of these
Fig. 84.
cells. The cell usually has a thin cell wall, which in living and growing cells incloses a colorless semifluid substance called protoplasm. This protoplasm is the living part of the plant. It is found in all the cells where growth is taking place, where plant substances are being made, or where energy is being transformed. It has the power of dividing and forming new cells, and it is in this way that the plants grow.
The little root hairs are one kind of plant cells. They consist of a thin cell wall within which is protoplasm and cell sap, a solution of different plant foods. Since the protoplasm and cell sap are denser than the soil water, more liquid moves into the cell than from it. A little of the cell solution does move out, however, and it is this which helps to dissolve the soil particles. The protoplasm in the cell regulates to some extent the interchange of liquids.
Experiment 93. -Cut off the stem of a thrifty geranium, begonia, or other plant an inch or two above the soil. Join the plant stem by a rubber tube to a glass tube a meter long, of about the same diameter as the stem. See that the rubber tube clings strongly to both glass tube and stem. It may be best to tie it tightly to these. Support the glass tube in a vertical position above the stem and pour into it sufficient water to rise above the rubber tube. Note the positionof the water column. Thoroughly water the soil about the plant. Watch the height of the water column, marking it every fewhours.
Fig. 85.
The water taken in by the roots passes on from cell to cell by osmotic action and rises in the stem in the same way that the water rose in the tube attached to the stem of the growing plant in Experiment 93. The root pressure, together with capillarity, as seen in Experiment 54, will account for the rise of the sap in lowly plants, but the cause of the rise of the sap to the top of lofty trees is difficult to understand.
Roots extend themselves through the soil by growing at the tips. Here the cells are rapidly dividing, forming new cells and building root tissue. As water is so essential, they are always seeking it and extending themselves in the direction where it is to be found. This causes themto extend broadly and to sink deeply (Fig. 86). A single oat plant has been found to have an entire root extension ofover 150 feet. This seeking of the roots for water sometimes causes the roots of trees to grow into drain pipes and stop them up. For this reason the planting of certain trees near sewer pipes isFig. 86.
often prohibited.
Experiment 94. -Boil some water so as to drive out the air and after it has become cool fill a 2-quart fruit jar half full. Dissolve in this all the necessary plant food as was done in Experiment 88, making the solution the same strength. Place in this a slip of Wandering Jew. Pour over the surface of the water a layer of castor oil or sweet oil. Place this jar alongside the slip in the other complete food solution, Experiment 88. Both slips have the same conditions except that the oil keeps out the air from the roots of one of them. Does the absence of air affect the growth of the slip?
As the tips of the roots are delicate, it can be readily seen that if they are to grow readily the soil around them must be mellow. It was also seen in Experiment 94, that if roots are to grow they must have air, another reason for keeping the soil mellow.
Roots are, however, not simply absorbers of water and dissolved food. Some of them act as storehouses for the food that the plant has prepared for future use. Beets, carrots, parsnips, turnips and sweet potatoes are examples of roots which store food ready for the rapid growth of the next year"s plant.
93.Stems.
Experiment 95. -Examine a corn stalk. Notice how and where the leaves are attached to the stem. Do the alternate leaves come from the same side of the stem? Cut a cross section of the stalk. Notice the outside hard rind, the soft pithy material and the small firmer points scattered about in the pith. Cut a section lengthwise of the stalk and notice how these small firmer points are related to the lengthwise structure of the stem.
Cut off a young growing corn stalk and place the cut end in water colored by eosin or red ink. Allow it to stand for some time and then cut the stalk off an inch or two above the surface of the water. How have "the firmer points" been affected? If possible, make the same observations and experiments on the stem of a small seedling palm tree.