116 PLANTS, THE FOOD OF ANIMALS 



which disappears after some time in the dark, but can be re- 

 formed in the light. Its chemical composition is very complex 

 and is of the nature of proteid, its formula being something 

 like C 4 4H 9 NPO 9 . 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 chlorophyll of the sun's rays richest in actinic energy. This 

 energy is utilized by the plant in decomposing CO 2 and H 2 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. 



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 fibrovascular 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 in the 

 formation of sugars and starch. For this process it was form- 

 erly supposed that a number of molecules of carbon were united 

 with twice as many molecules of water but now it is generally 

 believed that the base of the operation 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: N$R<> + N6CO 2 = NC 6 H 10 O 5 or starch. It is 

 more probable that the reaction is brought about through the 

 formation of intermediate products, thus: CO 2 + H 2 O = CH 2 O 

 + O 2 . Or possibly, CO2 + 3H 2 O = CH 2 O + 2H 2 2 , the lat- 

 ter, hydrogen peroxide, breaking down into H 2 O and O 2 . CH 2 O 



