UTILIZATION OF PLANT FOOD 31 



19. Function of Roots. — Hoots serve not only as an anchor- 

 age for the plant, to hold it upright and prevent its being 

 blown down or knocked over easily, but also as ports of 

 entry for water and plant food through the root hairs, and 'as 

 "aqueducts" or water carriers for the rest of their course. 

 The corky layer on the greater part of the roots prevents 

 loss of water and plant food on their way up into the plant. 



II. UTILIZATION OF PLANT FOOD 



20. Use of Inorganic Material. — Unlike animals, plants 

 manufacture carbonaceous or organic matter from inorganic 

 raw materials. All that the plant absorbs are inorganic 

 compounds dissolved in water. From these it makes its cells 

 and their contents, which latter are very complex and of many 

 different kinds. The basis of all the organic compounds in 

 plants is composed of carbon, hydrogen, and oxygen, and is 

 manufactured in the leaves for the most part. Energy for 

 this chemical synthesis is derived from the sun's rays. That 

 is, the energy of light waves is transformed into potential 

 energy in the form of chemical compounds. Only a few of 

 the light waves are useful in this work and of the sun's total 

 energy only 1 to 2 per cent, is utilized. 



21. The Spectrum. — The sun's rays are composed of 

 many kinds of light waves, some short and some long, some 

 visible and some not. Those that are visible can be separated 

 by a prism into a so-called spectrum which shows the colors 

 of the different waves from violet to red. The red waves 

 are almost twice as long as the violet waves. It is the 

 waves near the orange-red part of the spectrum that are 

 absorbed and changed to potential energy. 



22. Chlorophyl. — To absorb these light waves the plant 

 must have chlorophyl, which is a green substance manufac- 

 tured by the plant as soon as the plumule emerges into the 

 light. It is composed of two pigments, blue and yellow, if 

 not more. One of these pigments at least contains nitrogen 

 and phosphorus. They may be separated by appropriate 

 means, but their chemistry is little understood. This 



