THE PHYSIOLOGY OF PLANT-LIFE 15 



CHAPTER ir 



THE PHYSIOLOGY OF PLANT-LIFE: BEARING ON 



FOEMATION OF DEUGS AND POISONS 



Tlie central feature in the physiology of a green plant 

 is its power of capturing the energy contained in sun- 

 light, and of utilizing it to build up various complex 

 substances ultimately euluiinating in the formation of 

 living matter or protoplasm. The chlorophyll or green 

 colouring matter of plants arrests certain components of 

 the light which shines on it, and with the aid of the 

 energy thus obtained the protoplasm converts water and 

 carbonic acid into svrjar. The carbonic acid is derived 

 from the store which is always present in the atmos- 

 phere, as a result of which there is invariabl}'" a certain 

 amount of carbonic acid in solution in the water which 

 passes into the plant. The formation of sugar, however, 

 is only the first step. More raw materials are now 

 utilized, mainly from the soil in the form of phosphates, 

 nitrates, sulphates, &e. From these and the sugar the 

 plant builds up complicated nitrogenous organic bodies 

 called proteins. These all contain carbon, hydrogen, 

 oxygen, and nitrogen; some contain sulphur and phos- 

 phorus, and 'a few iron. They compose a large part of 

 the cpastituents of vegetable cells. They have not yet 

 been obtained in a pure form, and the very simplest of 

 them ha^ a complex structure. Their association with 

 protoplasm is very close, and it seems probable that the 

 formation of this substance, which is the physical bxsis 

 of life, is the culmination of a seres of changes of a 

 very complicated nature in the framework of the pro- 

 teins. How^ever formed, it is certain that the formatioii 

 of protoplasm is accomplished by the expenditure of 

 energy on the raw materials derived from the air and 



