MAPLE FAMILY 



substances whicli tlie }^laiU must needs discard are in the form ol 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 il 

 throH^n 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 ot \aluable matter is not a simple problem. These 

 substances contain nitrogen as a part of tlieir compounds, and as a consequence 

 are vevy readily broken down when exposed to the sunlight. In the living 

 normal leaf the green color forms a most effccti\e 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 ehlorophvlt. This \\-ouid allow the fierce rays of the September 

 sun to strilce directly through tlie broad expanse of the leaf, destroying all 

 within were not other means pr(i\ided for protection. In the first place, \\hen 

 thp chloroph\ll breaks dcswn, among tile resulting sul>stances formed is cyano- 

 phy'Il which absorljs the sim's rays in the same general manner as the chloro- 

 phyll. In addition the outer layer of cells of tlic leaf contains other pigments, 

 some ot which have been maslced bv the ehli>roiihyll and others \vhich arc 

 formed as decomposition products, so that the leaf exhibits outwardly a gor- 

 geous panoply of colors in veds, yellows, and bronzes that make up the autumnal 

 disi:)lay. 



At a time pre\ious to flic i:>cginning of the w ithdra\\al of the contents of the 

 leaf or the formation of the autuTimal colors, ]:)reparations ha\e been steadily in 

 progress for cutting away tlie leaf when tlic proper time should arri\'e. At 

 some point near tlie base of the leaf-stafk the formation of a lavcr of sjDecial 

 tissue had begun between (he woody cylinder in tlie centre and tlie thin epi- 

 dermis. When the time for the casting of the leaf arrives, this sjiecial tissue 

 grows ra|iidly, pushing apart or cutting the cells which have held the leaf 

 rigidly in position in such manner that finally the leafstalk at this point consists 

 of the brittle cylinder ol 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. MacDoug.\l. 



The gfeat leaf fall of the fiortherii states comes some time 

 betweeti the fifteetith and twetity-fffth a{ Octobei". As has 

 been e.xphiiiied the leaves have virtuall)' parted cotnpan}' 

 with the tree some time before ; they htive l)een 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 tibout the third week of October something 

 happens — it may be a wind or rain storm, a hetivy frost, or 

 two or three dtiys of excessively hot wetither — and then the 

 leaves come pourmg down in showers, and though the oaks 



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