118 PLANTS, THE FOOD OF ANIMALS 



ter, being something like 

 H 3 g). If white light be passed through a prism it is broken up 

 into the colors of the spectrum; if passed through a chlorophyll 

 solution it shows absorption bands in the red, yellow, green, 

 blue and violet, thus indicating the absorption by the chloro- 

 phyll of the sun's rays richest in actinic energy. This energy 

 is utilized by the plant in reducing C0 2 and H 2 O, a first step in 

 the manufacture of the plant's food. Chlorophyll, finally, is 

 easily split up into cyanophyll with a blue-green color, and 

 xanthophyll with a yellow color, while, in the presence of acid, 

 the Mg is replaced by hydrogen, giving a magnesium-free 

 yellow derivative, termed phaeophytin. 



GENERAL PHYSIOLOGY 



Food materials for the fern include a large variety of simple 

 elementary compounds found everywhere in the soil and air. 

 From the soil, salts of different kinds are absorbed by the roots, 

 and pass by means of the vascular bundles to all parts of the 

 plant; water, holding salts in solution, is also taken in by 

 these organs, and passes by osmosis and root pressure, aided by 

 evaporation in the leaves, to the highest parts of the aerial 

 plant. From the air, carbon dioxide and oxygen are taken in, 

 and by aid of the energy taken from sunlight, the carbon is 

 dragged away from the oxygen, and the hydrogen likewise 

 from oxygen, leaving these elements ready to recombine pre- 

 paratory to the formation of sugars and starch. For this proc- 

 ess it was formerly supposed that a number of molecules of 

 carbon were united with twice as many molecules of water, but 

 now it is considered more probable that the base of the opera- 

 tion is the hydroxyl OH. The reaction is usually expressed in 

 the following manner, although the equation does not represent 

 all of the actions taking place: n5H 2 O + n6C0 2 = nC 6 Hi 5 or 

 starch + n6O 2 . , It is more probable that the reaction is 

 brought about through the formation of intermediate products, 

 thus: C0 2 + H 2 O = CH 2 O + O 2 . Or possibly, CO 2 + 3H 2 O 

 = CH 2 + 2H 2 2 , the latter, hydrogen peroxide, breaking 

 down into H 2 O and O 2 . CH 2 O is a poison, formaldehyde, and 



