14 ELEMENTARY FORESTRY. 



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. Conifer- 

 ous trees transpire much less water than most deciduous trees: 

 frequently not over o roe-sixth as much. 



Mineral Substances are taken up in small quantities and con- 

 sist mostly of lime, magnesia and potash. They are carried 

 to ihe leaves where they are used ( perhaps also on their pas- 

 sage through the tree ) with a part of the water in food prepar- 

 ation. The main part of the mineral substances taken up re- 

 mains 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 

 no 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 in sufficient quantity even 

 if a portion of the leaf mould is carried away. If however 

 this removal is continued annually for a long period, any but 

 exceedingly fertile soils are likely to become exhausted just 

 as land on which field crops are grown cannot produce crops 

 forever without manuring. 



The Yearly Round of Life in a Tree. In the spring the tree 

 starts into growth and feeds on the plant food stored up the 

 preceding year; the leaves unfold and commence furnishing 

 plant food. These two sources of food push the growth along 

 very rapidly in the spring and early summer. By the first of 

 July the food stored up the previous season is exhausted in 



