6 GENERAL BOTANY 



all parts of the plant body may absorb oxygen. These life- 

 less substances of its environment are therefore continually 

 streaming into the plant from its surroundings through its 

 roots, stems, and leaves. The striking and characteristic thing 

 about the green plant is that it can take these simple, life- 

 less substances of the air and the soil and construct foot! from 

 them both for itself and for animals, and that, like animals, it 

 can build these inert foods into living substance, endowed with 

 the unique and characteristic properties of life. Within recent 

 times chemists have been able, in the chemical laboratory, to 

 compound such food substances as sugar and even simple forms 

 of nitrogenous substances or proteins; but no chemist has yet 

 been able to do what the plant does daily, namely, to convert 

 lifeless matter into living matter. The power of green plants 

 to make organic compounds is due to the fact that they have 

 a green substance, chlorophyll, within their tissues which enables 

 them to absorb and use the energy of light in \the making of 

 starch and sugar. When the streams of carbon dioxide pour 

 into the leaf from the air, they meet there the water derived by 

 the roots from the soil. In the presence of the green pigment, 

 chlorophyll, the living substance of the leaf is then able to 

 utilize the outside energy of the sun and unite the carbon of 

 the inflowing carbon dioxide (CO 2 ) with the hydrogen and 

 oxygen of the water (H 2 O) to make sugar and starch. The 

 sugar is then combined with the nitrogen, sulphur, and phos- 

 phorus, derived from soil salts which are absorbed by the roots, 

 into nitrogenous foods and ultimately into the living substance 

 of the plant body. 



A part of these foods, or, more probably, the living sub- 

 stance itself, is then broken down by union with the oxygen 

 which enters the plant at various points in the plant body and 

 brings about oxidation, or respiration, as in our own bodies. This 

 oxidation process resembles somewhat the oxidation which occurs 

 when coal is burned in a furnace or in a stove, and results in 

 the formation of cell energy and certain waste products in the 

 plant comparable to the heat, gases, and ash produced by the 

 combustion of coal and wood in a stove. This waste material 



