302 THE SCIENTIFIC MONTHLY
and in the Adirondacks. The very oldest metamorphosed 6edimenta.Tie& are mainly composed of shales containing carbon.
Since the carbohydrates constitute the basal energy supply of "ttie entire plant and animal world ,^° we may examine the process even inox^e closely than we have done above (p. 1T2). As a reservoir of life erier^^ which is liberated by oxidation, hydrogen exceeds any other demerit: in the heat it yields, namely, 34.5 calories per gram, while carbon yi^dfi 8.1 calories per gram.'® The results of the most recent researclx^s are presented by Wa<i:er.*^
The plaDt organ responds to the directive influence of light by a cux-^^rs^-ture which places it either in a direct line with the rays of light as in grass see^-cT lixigs, or at right angles to the light as in ordinary foliage leaves. . . . Of th^ 1.igbt that falls upon a green leaf a part is reflected from its surface, a part is "tx-^iiis- mitted, and another part is absorbed. That which is reflected and tranf* ar»::* i -tted giver, to the leaf its green color; that which is absorbed, consisting of <?c:* »--t:-aiB red, blue, and violet rays, is the source of the energy by means of whi <?• "!::». the leaf is enabled to carry on its work.
The extraordinary molecular complexity of chlorophyll has recently^ t>€eii
made clear to us by the researches of Willstatter and his pupils; Ushc^ -mT and Priestley and others have shown us something of what takes place in chloi-«:^;^>"fcyll when light acts upon it; and we are now beginning to realize more fuUj^ ^«?*rliat a very complex photo-Fonsitive system the chlorophyll must be, and how •mrMrm.vel^ has yet to be accomplished before we can picture to our minds wit^Xr*. -s^y degree of certainty the changes that take place when light is absorbed t»y i-fc. But the evidence afforded by the action of light upon other organic comp c:»^«.mcis?, especially those which, like chlorophyll, are fluorescent, and the conclusion a«^«:^-<?oi" cl- ing to modern physics teaching that we may regard it as practically c^^? -r'ta.in that the first stage in any photo-chemical reaction consists in the sepaz— ^a^t^ion, either partial or complete, of negative electrons under the influence of ligl^t, leads us to conjecture that, when absorbed by chlorophyll, the energy o '^ *^^^ light- waves becomes transformed into the energy of electrified particles a-xJd,
that this initiates a whole train of chemical reactions resulting in the ba m ^ cliog up of the complex organic molecules which are the ultimate products (^ ^^^ "^^ plant's activity.
Chlorophyll absorbs most vigorously the rays between B and ^^ ^ the solar spectrum,^^ which are the most energizing ; the effect or£ ^*^ rays between D and E is minimal ; while the rays beyond F again be^^^*^^-*^^ effective. As compared with the primitive bacteria in which nitr-^^^^^^^^ figures so largely, chlorophyllic plant tissues consist chiefly of car^^^^'"'
„ , ^c , o x-'o — lu- .'
while in some cases small amounts of nitrogen are found, and also w::m^^^' eral substances, potassium, magnesium, phosphorus, sulphur, and rr^-^^""
ganese. On the contrary, it is the invariable presence of nitro^^^
29 Moore, F. J., 1915, p. 213.
30 Henderson, Lawrence J., 1913, p. 245.
31 Wager, Harold, 1915, p. 468. 82Loeb, Jacques, 1906, p. 115.
S3 Pirsson, Louis V. and Schuchert, Charles, 1915, p. 164.
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