Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] BUDS AND STEMS 111 cotyledon we see the cut ends of the bundles in a cross section scattered through the pith. In the dicotyledonous stem the pathway of the colored fluid is much more definite with reference to the outside of the stem. Try to follow the lines out into the leaves or buds, tracing the course exactly. If the following experiment is made, it will be found that fluid passes not only up the stem but also down the stem. N.
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] BUDS AND STEMS 111 cotyledon we see the cut ends of the bundles in a cross section scattered through the pith. In the dicotyledonous stem the pathway of the colored fluid is much more definite with reference to the outside of the stem. Try to follow the lines out into the leaves or buds, tracing the course exactly. If the following experiment is made, it will be found that fluid passes not only up the stem but also down the stem. This experiment should be started several (at least two) weeks in advance. Place willow twigs in a glass of water. After a few days roots begi n to grow. Where do the roots appear ? After they have grown several da3^s (until the roots are one inch in length) girdle a twig by removing the bark in a ring about one inch in width. After a time, roots appear above the cut area and grow down to- ward the water. The lower roots below the girdled area die. This experiment shows us that the passage of food ma- terials evidently takes place in a downward direction just outside the wood in the layer of bark which contains the bast fibers and sieve tubes. Food substances are also con- ducted to a much less extent in the wood itself, and food passes from the inner bark to the inside of the tree by way of the pith plates or medullary rays. This can be proved by testing for starch in the medullary rays of young stems. It is found that much starch is stored in this part of the tree trunk. This experiment with the willow explains why it is that trees die, when girdled so as to cut the sieve tubes of the inner bark. The Apple twigs split to show the course of sap.
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