300 BIOLOGY 



ordinary life exhibit a great amount of active energy, they do 

 develop a little heat and a little motion, and they are constantly 

 lifting quantities of water from the soil to the tops of the 

 branches. All this requires energy, which is obtained by break- 

 ing down some of the starch and utilizing the energy thus lib- 

 erated. 2. Plants are always at work building other materials 

 besides starch. Proteids, woods, and fats are manufactured by 

 combining, within the living cells, the various materials ab- 

 sorbed by the roots (nitrates, etc.), with the starches made in 

 the leaves. The chemical processes by which these new organic 

 compounds are built are not yet understood, but one feature 

 is significant. Just as starches are more complex than the 

 water and carbon dioxid out of which they are made, so the 

 proteids are far more complex than the starches, nitrates, etc., 

 out of which they are made. Since it requires energy to build 

 the complex molecule starch out of the simpler carbon dioxid 

 and water, so too it requires energy to build proteids out of 

 the starches and nitrates. For this purpose the plants do not 

 use the sun's rays directly, but they use the energy they have 

 stored in the starch. In other words, in making proteids, a cer- 

 tain quantity of starch or sugar is broken down into a condition 

 of carbon dioxid and water, and as a result of this destruction 

 the stored energy in the sugar molecule is liberated. This 

 energy is liberated within the living cells, and under such 

 conditions the protoplasm can make use of it for building the 

 complex proteids out of the simpler materials. This general 

 process is called metastasis. 



Thus it is seen that the plant protoplasm uses the starches 

 for a double purpose. Part of them are reduced to the condi- 

 tion of carbon dioxid and water in order to liberate the energy 

 needed by the plant. Part of them are combined with other 

 ingredients to enter into the combination of proteids, etc. By 

 this latter process there is thus (1) an accumulation of proteids 

 and other substances in the plant body, (2) a destruction of 

 sugar or starch, (3) an elimination of carbon dioxid and water, 



