Composition of the Leaves of Some Forest Trees

Nine deciduous trees, each of a different species (Table 1), were selected on the campus of the Minnesota Agricultural Experiment Station and five collections of leaves made from each. All the trees were within 300 yards of the laboratory and all on the same soil type Thurston loam, a soil on which alfalfa and sweet clover thrive without application of lime. The first collection was made on June 1, 1933, all the trees being then in full leaf and the following three on July 1, August 1, and September 1. On these four dates the leaves were plucked from .the lowest branches. In the fifth and final collection from each tree, made as early in October as the greater portion of its leaves had fallen, a large sample was gathered from the ground beneath the tree, the leaves being picked up one by one so as to avoid including any from other species. In. the case of the bur oak the last collection was made on October 11 while with the other trees it had to be deferred until October 16, as the leaves did not fall freely until after the first killing frost, which occurred October 13. After September 25 there was no precipitation until October 15, when a, beating rain, amounting to 1.18 inch, brought to the ground nearly all of the remaining leaves except in the case of the white oak and red oak. Even with these