To verify the existence of osmotic water transfer, or, as some say, root pressure, can be directly in the field or in the garden. Find some fast growing plants, preferably with a strong and wide enough stem (sunflower, nettle, Tulip, etc) and cut it to the height of about 10 cm above the ground. Sticking out of the ground stalk wear short rubber tube into which is inserted a thin and long, not less than half a meter, glass tube. Clearly, such a long tube needs to fix; tie her to the stake, driven near to the earth. For the best seal wrap a rubber tube with a thread in the place where it attaches to the stalk, but you can also coat the joint with clay, so that the sealing is reliable.
Now do some watering, and soon the water will begin to rise in the tube. If the tube diameter is not more than 5 mm , the water column is high.
But the osmotic pressure is not the only reason by which water in plants is moving upwards. Among other reasons - transpiration, i.e. the evaporation of water leaves. Giving nutrients to the plants, water through the stomata of the leaves evaporates, and in its place comes a new portion of water from the roots. Experience with transpiration simple. Put in a test tube with water, cut a sprig of some plants mark on the tube the water level (at least bandaging her in this place colored thread), and soon you will notice that lowered the water level in the tube. But maybe the reason is that water evaporates directly from the tube?
To prevent direct evaporation, pour on the surface of the water a little bit of vaseline or vegetable oil: it will completely cover the surface, preventing evaporation. However, the water level in this case will be dropped. Therefore, the water evaporates through the leaves. If you have the scale, experience with transpiration can be accelerated and made more clear: the tube with the branch (not sure about a few drops of oil on the surface, put on a Cup of scales and trim. Soon the balance will be broken, and the Cup, on which stand the tube will rise up.
Similar experiences can be supplied with different plants, Pets flowers: the rate of transpiration from them will be different. But try to slightly modify the experience: make a branch plant of the inverted glass jar. You can not even cut for this experience and just cover the jar any small houseplant, for example, a young nasturtium. If the plant is watered properly, in a confined space, the atmosphere will soon be filled with water vapor, and the water will not evaporate from the leaves. Transpiration is known not to exist, however, some time later appear on leaves water droplets. Why? Again began to work osmotic pressure...
And the water rises along the stem due to the fact that the plant is permeated by the finest vessels - capillaries, in which the liquid moves up faster than they are thinner. If you had a glass capillary with a diameter of 0.02 mm , the water could rise by him to three meters! And in plants there are capillaries and thinner...
Several glass jars, pour the water and podcasta her a few drops of ink. The stems or branches of different plants cut with a sharp knife (preferably under water) and put in jars. Little by little tinted water will fill all the vessels of plants, will rise by capillarity. To detect its movement easily change the color of the veins on the leaves. If you make each branch a few cross sections, you will see how are the capillaries (we recommend to take for this purpose Lupu stronger).
And last experience with plants. Water, colored ink, pour in any large container, for example, in a bowl. The branch will lower into the water and cut under water part of the stem. After a few minutes, remove the branch and make a sharp knife a few slices. For a few minutes (don't forget to mention, how much water is quite high will move along the stem.
Another, the same branch cut on the air, and then immerse in the same bowl and keep as many W e minutes in the water. This time, as shown by the sections, the water rose much lower!
The reason is that the capillaries of the plants are very thin, they are easily clogged air tubes - tiny bubbles. And then the supply of water to the leaves stops. And when the stem is cut under water, the air tubes nowhere to take.
Perhaps you now understand the meaning of the Council, which give the experienced florists: if you want cut flowers stood in a vase as long as possible, cut the stems are not on the air, and under water.