108 APPLIED BIOLOGY 



cambium is that a branch of a grape-vine girdled between a 

 bunch of grapes and the root will produce better fruit on that 

 branch, because the foods from the leaves are kept from going 

 on down the stem. Of course, such a girdled branch will be 

 useless in the next fruiting season, but since grapes are 

 always developed on new shoots, it is the common practice 

 to prune away each winter most of the branches which bore 

 fruit in the preceding summer. 



It is possible for foods to go up a stem. The leafy branch 

 above a bunch of grapes might be cut off and the grapes 

 continue to grow from foods coming up the stem in the wood- 

 tubes from other branches with leaves. In the spring 

 before leaves appear on trees and shrubs, foods go up the 

 stem from the cells in root or stem where they were stored 

 during the winter. If a branch of a tree be cut off in winter 

 just above a bud, this bud will usually grow rapidly in the 

 following spring and form a large branch. Orchardists 

 make use of this fact when they prune trees. All these 

 cases prove that the foods must be able to go up the stem. 

 By removing girdles of bark it can be demonstrated that 

 the upward movement is in the wood-tubes. 



It is evident from the experiments described in the above 

 paragraphs that foods in solution in water may be transported 

 either up or down the stem, depending upon where the supply 

 is located and where needed. 



104. Use of Foods Transported from Leaves. The 

 dissolved sugars and other more elaborated foods made in 

 the leaves may be used in the plant in two ways, as follows : 



(1) Used by Cells. We have seen that living plants re- 

 quire food, and this is true of every living cell. Some of 

 the food from the leaves is at once used by cells in roots, 

 stem, flowers, or developing fruits. Part of the food un- 

 doubtedly goes to make new particles of living matter 

 (protoplasm) to replace that continually being worn out and 

 made lifeless. It should be kept in mind that a living plant 



