MAPLE FAMILY 
substances which the plant must needs discard are in the form of nearly insolu- 
able crystals, and by remaining in position ‘n the leaf drop with it to the ground. 
The plastic substances within the leaf which would be a loss to the plant if 
thrown away undergo quite a different series of changes. These substances are 
in the extremest parts of the leaf, and to pass into the plant body must penetrate 
many hundreds of membranes of diffusion into the long conducting cells around 
the ribs or nerves, and then down into the twigs or stems. The successful 
retreat of this great mass of valuable matter is not asimple problem. These 
substances contain nitrogen as a part of their compounds, and as a consequence 
are very readily broken down when exposed to the sunlight. In the living 
normal leaf the green color forms a most effective shield from the action of the 
sun, but when the retreat is begun, one of the first steps results in the disinte- 
gration of the chlorophyll. This would allow the fierce rays of the September 
sun to strike directly through the broad expanse of the leaf, destroying all 
within were not other means provided for protection. In the first place, when 
the chlorophyll breaks down, among the resulting substances formed is cyano- 
phyll which absorbs the sun's rays in the same general manner as the chloro- 
phyll. In addition the outer layer of cells of the leaf contains other pigments, 
some of which have been masked by the chlorophyll and others which are 
formed as decomposition products, so that the leaf exhibits outwardly a gor- 
geous panoply of colors in reds, yellows, and bronzes that make up the autumnal 
display. 
At a time previous to the beginning of the withdrawal of the contents of the 
leaf or the formation of the autumnal colors, preparations have been steadily in 
progress for cutting away the leaf when the proper time should arrive. At 
some point near the base of the leaf-stalk the formation of a layer of special 
tissue had begun between the woody cylinder in the centre and the thin epi- 
dermis. When the time for the casting of the leaf arrives, this special tissue 
grows rapidly, pushing apart or cutting the cells which have held the leaf 
rigidly in position in such manner that finally the leaf stalk at this point consists 
of the brittle cylinder of wood surrounded by the loosely adherent cells of this 
newly formed layer of separation. ‘The merest touch or breath of air will split 
the layer of separation, break the wood, and allow the leaf to fall to the ground. 
—D. T. MacDouGat. 
The great leaf fall of the northern states comes some time 
between the fifteenth and twenty-fifth of October. As has 
been explained the leaves have virtually parted company 
with the tree some time before; they have been falling 
since the first, and the ground is strewn with them, but as 
you look at the trees they show no perceptible diminution of 
foliage. But about the third week of October something 
happens—it may be a wind or rain storm, a heavy frost, or 
two or three days of excessively hot weather—and then the 
leaves come pouring down in showers, and though the oaks 
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