HERMAN H. CHAPMAN 25 



tion from the pores or stomata and evaporation through the 

 cuticle. It enables the green and delicate tissues of the 

 leaf to maintain their rigidity. The loss of too much water 

 is shown by wilting, and if not supplied, the leaves would 

 die. The elaboration of food from the carbon dioxide of 

 the air by the aid of the chlorophyll bodies requires water, 

 and the food or carbohydrates thus formed as starch is 

 redissolved for transportation in solution to other portions 

 of the tree where growth of wood occurs. Thus the water 

 supply of the roots is of the first importance. There can 

 be too much water in the soil. Roots need air as well as 

 water, and cannot perform their functions properly in a 

 soil constantly below the water level. 



The Characteristics of Soils Affecting Soil Moisture. — 

 Swampy soils are not as favorable for trees as better 

 drained soils. The most favorable sites are the well- 

 drained loamy soils which will hold a large amount of water 

 by capillary attraction, and are elevated far enough above 

 the level of the underground water table so that the roots 

 at the same time have plenty of air. The mechanical com- 

 position of soils is important, since it determines very large- 

 ly their behavior toward water. The larger the soil par- 

 ticles the less water the soil will hold. The series used in 

 such soil classifications is gravel, sand, loam, silt and clay. 

 There is a disadvantage in a clay soil since the particles 

 are so finely divided that the water is held tenaciously and 

 the soil remains cold and wet, while if it does dry out it 

 bakes hard and cracks. Loamy soils, with particles about 

 midway in size between sand and clay, allow a free move- 

 ment of water, retain it in sufficient quantities for tree 

 growth and allow a proper circulation of air. 



The depth of the soil of course affects its moisture hold- 

 ing capacity. A shallow soil over a rocky ledge is a dry 

 soil since there is no storage room for water. But a very 

 deep soil, if sandy, may be still drier, since the water rap- 

 idly percolates through it to depths where even tree roots 



