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.B. 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 gro w . 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. 



