CONSUMPTION OF LIGHT BY PLANTS. 459 



In a dark place, then, it is possible for a seed to grow, but it grows in 

 a certain way, and only to a certain extent. Its stem and its leaves are 

 of a sickly yellowish hue: exposure to the sunshine soon produces a 

 green color in these parts, and the weight of the plant increases. Growth 

 in darkness leads to one result, and growth in the sunshine to another. 



From these facts it therefore might appear, from a superficial considx 

 eration of the thing, that the development of a plant depends p art i a i infer- 

 on two distinct conditions an innate power which resides ence respecting 



-T 1,1 ,- P-I.-I-I T the existence 



in the germ, by the action of which the matters previously ofapiastio 

 stored up in the- seed by the parent plant are regrouped, and P wer - 

 so arranged as to constitute a new organization ; but this power does not 

 extend tg the obtaining of new material; it is only a power of arrange- 

 ment a PLASTIC POWER. Whatever new material is required must be 

 furnished by a totally distinct agency, the sunlight; and just as the 

 plastic power can not collect, the sunlight can not arrange. Each has 

 its own sphere of duty. The one gives the substance, the other 

 moulds it. 



Every flowering plant, no matter how humble it may be, is, then, a rep- 

 resentative of the action of these double influences, and, when Consumption 

 properly considered, may well extend the views we ought to yegetabie* 

 entertain of the system of nature. The supplying or furnish- development, 

 ing agent, the light, comes from a star which is at a distance of almost a 

 hundred millions of miles, and is the pivot of all the planetary motions. 

 Without this extraneous, this foreign force, the whole surface of the earth 

 would be a desolate waste, presenting no semblance of life. The leaf, 

 the flower, the bud, the stem, the root, are all made of substance that has 

 been given by the sun, derived, it is true, from one of the constituents 

 of the air, but forced to take on the special state which suits the needs 

 of the plastic power by that distant agent ; and, in order for this to oc- 

 cur, it is plain, from mechanical considerations, that there must have been 

 an expenditure of power, or of the acting principle itself, for light can 

 not produce these effects without losing its own peculiar form. For the 

 decomposition of a given weight of carbonic acid, and the formation of a 

 given weight of gum, a fixed and invariable quantity of light is required ; 

 just as it is necessary, in moving a mass of a certain weight, to expend an 

 equivalent and definite 'force. So the substance of which plant-organs 

 consist has been brought into an available state by the consumption of 

 a definite quantity of light perhaps its incorporation, under some other 

 form, in the resulting mass. It may be pent up and imprisoned in the 

 organic structure for any imaginable time, even for centuries, but is ever 

 ready to resume its primitive state when favorable circumstances exist. 

 The coal-fields which furnish us with fuel are the remains of primeval 

 forests which grew in the ultra-tropical climate of the secondary times, 



