20 FUNDAMENTALS OF FRUIT PRODUCTION 



even weeks after the transplanting operation and that, therefore, the 

 tree must be kept practically dormant until it is actually planted. This 

 may be done by holding it at a low temperature in shade, or, if suitable 

 storage facilities are not available, by repeatedly lifting and immediately 

 heeling in again. The effect of the low temperature is to keep the tree 

 dormant because no top growth will take place at a temperature approxi- 

 mating the freezing point. The effect of the repeated lifting and heeling 

 in again is to check growth of the top by preventing the formation of new 

 roots and root hairs though the temperature may be suitable for their 

 development and thus cutting off the tree's water supply without which 

 the shoots are retarded. 



It is necessary to move evergreen trees of any considerable size, like 

 the pine or the orange or the avocado, with a ball of earth so that at least 

 a moderate portion of the real water absorbing organs of the plants are 

 retained and remain active; otherwise, the foliage wilts or falls off and 

 the plant is likely to die. The facts that have been presented explain 

 why excessive watering will not make up for the loss of roots, and particu- 

 larly of root hairs, by trees transplanted during their growing season. 

 Though their remaining roots may be surrounded by a nearly saturated 

 soil they cannot take up appreciable quantities of this moisture. 



The Water Absorbing Process. — The process by which water is absorbed by 

 the root hairs is osmosis. A plant cell such as the epidermal cell of a root with a 

 root hair attached has a cell wall Hned with protoplasm surrounding a central 

 vacuole. When the root hair comes in contact with the moisture of the soil an 

 osmotic system is established and the protoplasm of the root hair becomes a 

 semi-permeable membrane separating two solutions, the soil solution on the 

 outside and the vacuole on the inside. These two solutions have different 

 concentrations, that of the vacuole being greater than that of the soil solution; 

 in other words there is less water in the vacuole than in a corresponding volume 

 of soil solution. To equalize the concentrations of water on either side of the 

 membrane water passes from the soil into the vacuole. 



The absorption of water in this way by the cell must increase the size of the 

 vacuole and therefore induce a simultaneous distention of the cell wall. Eventu- 

 ally the elasticity of the cell wall will exert such a pressure on the vacuole that 

 no more water can be absorbed and there is a balance between the elasticity of 

 the cell wall and the osmotic pressure of the cell contents; the cell is in a state of 

 turgidity. Under ordinary conditions all the living cells of a plant are turgid, 

 but this turgidity may be lost, either by an increase in the plasticity of the cell 

 wall or by the loss of water from the vacuole. Either process destroys the 

 balance on which turgidity depends. 



Factors Enabling the Root to Exploit the Soil. — Several factors cooperate in 

 enabling the plant to exploit the moisture content of the soil. The root hairs are 

 continuously formed anew at a certain distance from the tip of the growing root 

 so that a new supply is produced as fast as the older root hairs die. As these 

 extend into untouched portions of the soil, the roots are continually pushing into 



