62 Principles of Plant Culture. 



forms just outside the union of the bark and wood. In 

 all plants having more than one cotyledon (46), this cur- 

 rent is through the inner layers of the bark. The pre- 

 pared food matter is dissolved in the water that saturates 

 the cell- walls, and passes from the leaves to other parts 

 of the plant by diffusion (64). 



81. Killing Trees by Girdling. To destroy the life of a 

 tree that can not be conveniently 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 (78) 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 cutting 

 off both the ascending and descending currents, death of 

 the tree soon follows. 



82. 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 satisfac- 

 tory growth the first season. 



