THE GENERAL CHEMISTRY AND PHYSICS OF PLANT- LIFE. 257 



tioii of O. This true respiration is, in general, necessary for the life 

 and growth of plants. Based npon the investigations of Boussusr- 

 GAULT, Gakreau, Sachs, Pasteue, Nageli, and Pfeffer, we may for- 

 mulate our present knowledge in regard to this subject as follows. 



1. If we consider the chemistry of fermentation in plants (the 

 conversion of sugar into CO^ and alcohol, and other similar processes) 

 as " intramolecuhir respiration," ' we may make the general state- 

 ment that DO plant can live without respiration. 



2. Some of the energies necessary to cell-hfe are due to respira- 

 tion. 



3. Oxygen is also necessary for the existence of some fungi if 

 they are not supplied with substances capable of undergoing fer- 

 mentation. Fermentation enables them to exist without the respi- 

 ration of O ; without fermentation growth ceases unless oxygen is 

 supplied. 



4. Respiration continues as long as the normal conditions of life 

 exist ; it is most active in the growing plants and growing parts of 

 plants; for example, during germination and during the develop- 

 ment of tubers and buds. Within certain limits respiration increases 

 with the rise of temperature. A direct influence of light upon the 

 respiration of chlorophyll-less parts of plants has not been observed. 

 Chlorophyll-bearing parts of plants assimilate only in the presence 

 of sunlight, but respire in the dark as well as in the sunlight. 



" Selection?^ 



We usually speak of plants as having the ability to " select " 

 certain food-substances. The true explanation of the meaning of 

 this term is as follows. It has been known for a long time that dif- 

 ferent plants growing in the same environment take up the same 

 food-substances in different proportions ; for example, Nijinpha^a 

 alha and Atnindo j^hragniites, both of which grow in water or in 

 marshy soil, and which are therefore in contact with the same 

 soluble food-substances, take up SiOJn widely different proportions. 

 The former plant contains usually less than i per cent of silica, the 

 latter usually more than 71 per cent (Schultz-Flketh). From un- 



' According to Pfluger (1875), iutramolecular respiration takes place in an 

 atmosphere free from oxygen with liberation of CO^ due to the breaking up of 

 compounds within the cell ; "normal" respiration is accompanied by oxygen- 

 assimilaliou. 



