1s ELEMENTARY FORESTRY. 
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 deciduous 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 (pei:haps also on their passage 
through the tree), with a part of the water, in food preparation. 
The main part of the mineral substances 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 leit 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 con- 
tinue 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 exceed- 
ingly 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 carly summer. By the first of 
July the food stored up the previous season is exhausted in 
many trees, and growth is entirely dependent upon the food fur- 
