CHAPTER II 



The subject of metabolism, that is, of the farther transformations 

 of primary organic substances, and the fact of respiration, have been 

 referred to already. Gels' " Experimental Plant Physiology " sug- 

 gests many experiments under this head. Kerner, in Vol. I, Part 2 f 

 of his "Natural History of Plants," classifies these products as fol- 

 lows : under building materials as albumens (albumen, casein 

 fibrin, etc.), cellulose (changed sometimes to lignin or cork) and 

 starch (a mixture of cellulose and granulose) ; and under accessory 

 substances, pigments, including chlorophyll, sweet-tasting substances, 

 oils, resins, balsams, fats, alkaloids (nicotine, quinine, etc.), gluco- 

 sides (saponin, tannin, etc.), organic acids, organic salts, amides and 

 ferments. But the subject seems hardly suitable for children. They 

 can of course think of various plant products, and can reason out the 

 fact that the building materials originating in the leaves must be 

 transported to any part of the plant requiring food or acting as a 

 store-house. So it becomes apparent that, besides the ascending cur- 

 rent of raw material, there is also a stream carrying organic food, 

 whose direction is in the main downward. The movement of this 

 stream is explained by the law of diffusion. As any cell uses up 

 material, the same material will be at once replaced from a contigu- 

 ous cell, which cell repairs losses from the next cell and so on. The 

 sets of cells through which this distributing current passes will be 

 referred to in the supplement to Chapter VIII. when the subject of 

 the division of labor among the cells will be further emphasized. The 

 fact that metabolism and growth go on even better in darkness seems 

 to be thoroughly established by means of experiments. It is found 

 that the greatest daily growth is usually just before sunrise. 



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