The Water of Plants and its Movements. 63 



80. Killing Trees by Girdling. To destroy the life 

 of a tree that can not be conviently removed, we girdle 

 it by cutting a notch about the trunk beneath the lowest 

 branch. This cuts off the downward food current and 

 so starves the protoplasm of the roots. If the notch is 

 made after the leaves have expanded in spring, and ex- 

 tends only through the bark, the leaves may remain 

 fresh for several weeks, for the transpiration current 

 passing through the sap-wood (77) may continue. 

 Since the roots receive no nourishment, however, they 

 will soon cease to grow and will usually die from starva- 

 tion before the following spring. If the notch is cut 

 deep enough to reach through the sap-wood, thus cut- 

 ting off both the ascending and descending currents, 

 death of the tree soon follows. 



81. Root Starvation may occur Without Girdling. 

 In seasons of extreme drought, when the leaves are 

 poorly supplied with crude food materials from the soil, 

 the amount of prepared food may be so" meagre that 

 the food current will be exhausted before it reaches the 

 roots. In such cases the roots perish, and the tree is 

 found dead the following spring. This most frequently 

 occurs with trees on poor soil, that have suffered from 

 insect attacks as well as from a dearth of water. It 

 often occurs also in recently-transplanted trees that 

 fail to make satisfactory growth the first season. 



82. To Destroy the most persistent Weeds we starve 

 the roots by preventing all leaf growth (339). 



83. Restriction of the Growth Current Promotes 

 Fruitfulness by causing an accumulation of prepared 

 food in the stem and branches (134 B). 



