2 3 8 



PART III. VEGETABLE PHYSIOLOGY. 



sition of this carbo-hydrate, we do not know, nor do we know 

 precisely the process of its formation, or of the production of 

 proteid matter from it, but we know it is made from carbon-diox- 

 ide and water. 



Since the molecules of carbon-dioxide and water contain 

 more oxygen than is required in the construction of the mole- 

 cule of a carbo-hydrate, a portion of it escapes from the plant as 

 free oxygen. Suppose, for example, the carbo-hydrate be repre- 

 sented by the formula C 6 H 10 O 5 we may express the formation 

 of its molecule by the following equation: 6C0 2 -|-5H20=C 6 

 H,o0 5 +60. 2 . In this case, it will be seen, six molecules of oxy- 

 gen, or as much as is contained in the carbon dioxide used, 

 become free, and it is evident that an amount equivalent to this 

 would be set free in any case, whatever the carbo-hydrate formed. 

 The equation, however, must not be taken to express the process 

 which actually takes place, for the reactions are probably much 

 more complicated than this would imply. 



The deoxidizing power which the chlorophyll plant possesses 

 is of the highest significance, so far as the maintenance of life is 

 concerned. Animals are continual consumers of oxygen and 

 generators of carbon-dioxide, and if there were no means of 

 setting free again the oxygen they are continually bringing into 

 combination, the atmosphere would soon become poisonous and 

 unfit to sustain animal life ; but plants, by feeding upon the car- 

 bon-dioxide which animals exhale, and restoring the oxygen 

 which they consume, maintain the atmosphere at nearly a con- 

 stant composition, and the balance of life is kept in equilibrium. 



It was formerly supposed that the starch granules found in 

 the interior of the chlorophyll-bodies were the direct result of 

 the assimilation of carbon-dioxide and water, but the investi- 

 gations of Strasburger and others clearly prove that this is not 

 the case. They are formed from protoplasm, the latter substance 

 being broken down by the agency of the chlorophyll into this 

 and other products. It is probable also that that formed by 

 amyoplasts in chlorophylless cells is also produced from proteid 

 matter. Its formation, therefore, might be regarded as belong- 

 ing rather to the destructive than to the constructive processes 

 of the plant ; the breaking down, however, is only preparatory 

 to reconstruction; for starch is one of the most important of the 



