THE TREE. 9 



of foliage at work, amount of light at its disposal, climatic 

 conditions, and the condition of tree-growth. The amount 

 of water transpired is so large in comparison to the amount 

 retained in the tree that while an acre of forest may store 

 in its trees 1,000 pounds of carbon, 15 or 20 pounds of min- 

 eral substances, and 5,000 pounds of water in a year, it may 

 have taken from the soil and given off to the air from 

 500,000 to 1,500,000 pounds of water, or from one-quarter 

 to one-half as much as agricultural crops. It has been 

 estimated that the leaves of deciduous trees transpire one- 

 sixth to one-third as much water as an equal surface of 

 water. Large deciduous trees undoubtedly give off as 

 much as a barrel of water a day in dry summer weather. 

 Coniferous trees transpire much less water than most de- 

 ciduous trees, frequently not over one-sixth as much. 



Mineral Substances are taken up in small quantities and 

 consist mostly of lime, magnesia, and potash. They are 

 carried to the leaves, where they are used (perhaps also on 

 their passage through the tree), with a part of the water, 

 in food preparation. The main part of the mineral sub- 

 stances taken up remains as the water transpires in the 

 leaves and young twigs and is returned to the soil when the 

 leaves are shed and when the tree is cut and the brush left 

 to decompose and make humus. 



The Soil of Woodlands is Improved from year to year if 

 the leaves and litter are allowed to remain on the ground 

 and fire is kept out, since the mineral matters taken 

 up by the tree are largely returned to the soil in a 

 more soluble form and the amount of humus is increased. 

 For this reason there is little need of alternating woodland 

 crops. 



Almost any soil can furnish a sufficient quantity of 

 mineral substances for the production of a crop of trees, 

 provided it is moist and the leaf mould is not removed. 

 Good soils will continue to furnish mineral matter jn suffi- 



