THE METABOLISM OF PLANTS. 159 



the leaves of the following plants under as nearly as possible 

 the same conditions. The following are his results : 



Tropceolum majus . . 4466 grammes. 



Phaseolus multiflorus . 3*215 



Ricinus communis . . 5^292 



Helianthus annuus . . 5*559 



We are now in a position to compare the constructive 

 capacity of plants which contain chlorophyll, of plants which 

 do not contain chlorophyll, and of animals. The first of the 

 series of synthetic processes which we have traced above, the 

 formation of non-nitrogenous organic substance from carbon 

 dioxide and water, can only be effected by organisms (animals 

 as well as plants, according to the observations of Geddes) 

 which contain chlorophyll, and with this we must correlate the 

 production of starch. The second process, the formation of 

 proteid from organic non-nitrogenous carbon-compounds and 

 inorganic salts containing nitrogen and sulphur, can, appa- 

 rently, be performed by all plants alike, but it cannot, so far 

 as we know, be performed by animals, excepting, possibly, 

 those which contain chlorophyll. Stating the case in the most 

 general terms, we may say that whereas a plant is nourished 

 when nitrogen is supplied to it in the form of inorganic salts, 

 an animal can only assimilate nitrogen in the form of proteid. 



The last of all the processes of constructive metabolism 

 yet remains to be considered, the conversion of dead unor- 

 ganised proteid into living organised protoplasm. This must 

 take place in every cell so long as it is living, and it must 

 necessarily accompany the formation of new. cells. But little 

 can be said as to t}ie nature of this process, for our knowledge 

 of the differences between dead proteid and living protoplasm 

 is very slight. We are indeed acquainted with certain facts ; 

 we know, for instance, that the primordial utricle of dead cells 

 readily allows of the passage into it and through it of sub- 

 stances which could riot enter or pass through it in life (p. 44); 

 that the interchange of gases between the cell and the 

 atmosphere which goes on so actively during life, and which is 

 the expression of unceasing chemical combination and decom- 

 ' position, is arrested ; that the evolution* of energy in the form 



