148 BOTANY FOR BEGINNERS CHAP. 



is one of the problems of plant physiology which requires 

 solving. 



The following experiments will demonstrate how the sap 

 travels in woody plants. 



EXPT. 140. Obtain a woody plant, such as an Oak, which is grow- 

 ing in a pot. (a) From one branch remove a ring of tissue down as 

 far as the new wood, i.e., cut away the bark cortex and phloem, and 

 pack the wound with cotton wool to prevent the entrance of fungi. 

 (b) From another branch remove a ring of the new wood, and replace 

 the bark and cortex. Note 



(i) The leaves on the branch, which has only a ring of tissue removed, 

 down to the new wood, are still green and fresh. 



(ii) The leaves on the branch, which has had the new wood removed, 

 have flagged ; they ultimately die. 



(iii) The water, which makes good that lost by transpiration, travels 

 in the new wood, but neither in the cortex nor in the bark. 



EXPT. 141. In many parts of the country old trees may be seen 

 which have lost their heart wood, as well as the outer tissues of the 

 plant. When such a tree is encountered, the following observations 

 should be made. Note 



(i) That leaves are still produced on the upper part of the old stem. 



(ii) That the leaves are green and fresh. 



(iii) These leaves must be supplied with water. This can only take 

 place through the new wood, because the heart wood and the outer 

 part of the tree have decayed. The water travels only through the new 

 wood. 



How the Elaborated Sap Travels in Plants. The 

 sap which is acted on in the leaves by the chlorophyll and proto- 

 plasm, and which becomes very rich in organic compounds, is 

 called elaborated sap. This is distributed to those parts of 

 the plant where growth is going on, or where reserve material 

 is stored up. How is this elaborated sap distributed ? If a 

 leaf is examined the xylem will be found distributed over the 

 upper surface of the leaf, and the phloem on the under side. 

 The xylem brings water and minerals in solution to the cells of 

 the leaf ; when this has undergone the necessary changes, and is 

 fit for the nourishment of the plant, it is carried away down the 

 phloem. Different materials are produced in the leaf by the 

 activity of the chloroplasts and protoplasm. These materials 

 can be divided into proteids, fats, and carbohydrates (p. 85-7). 

 Each of these is distributed in a different way throughout the 

 plant. The proteid substances in the elaborated sap travel 



