178 



THE LIFE OF THE PLANT 



roots, using for the purpose the same method as we 

 used in determining the course of the rising sap. Let 



us make a circular cut in 

 the rind right down to 

 the cambium, as is shown 

 in fig. 51, and place our 

 branch in water for several 

 weeks. We shall notice 

 that the roots will appear 

 this time not at the lower 

 part of the stem, but at 

 the upper edge of the 

 circular cut ; in cutting 

 across the rind we have 

 evidently barred the way 

 for the nutrient sub- 

 stances which moved 

 down the stem. It follows 

 that the circular cut in 

 the rind, which does not 

 hinder the ascent of the 

 sap from the root, com- 



FIG. 51. 



pletely stops the sap 



moving in the opposite direction. This means that 

 whereas the sap rising from the root passes by way of 

 the wood, the sap coming from the leaves passes by 

 way of the rind. 



The truth of this inference is also proved by another 

 experiment. Let us choose a branch of some plant, on 

 which fruit has only just begun to set, and let us 

 cut a ring in the bark between the fruit and the near- 

 est leaves : the fruit will cease to develop. Thus 

 the circular cut in the rind, which separates an organ, 

 such as the root or the fruit, from the leaves it feeds 

 on, will deprive that organ of the very possibility of 

 development. We have therefore proved beyond doubt 

 that the nutrient substances serving to build up the 



