THE CHLOROPHYLL APPARATUS 163 



the temperature. Inhibition can be caused also by the 

 accumulation of the products of the activity of the plastide, 

 a concentration of the sugar amounting to 8 per cent, being 

 sufficient to bring it about. 



The mechanism is an exceedingly delicate one and can 

 be thrown out of gear by various external agencies. Ewart 

 has shown that it can be inhibited by heat, cold, desiccation, 

 partial asphyxiation, prolonged insolation, and by the action 

 of dilute alkalies or mineral acids. 



We mentioned at the commencement of this chapter 

 that the chlorophyll apparatus is concerned in the manu- 

 facture of almost the whole of the organic material of the 

 globe. In a few humble organisms the construction of 

 such material can proceed without its help. These are 

 certain bacteria which can transform ammonia compounds 

 into salts of nitrous and nitric acids, growing and multi- 

 plying at the expense of the products they thus obtain, 

 together with carbon dioxide. There are two kinds of 

 these bacteria, one of which oxidises ammonia to nitrous 

 acid and the other converts this into nitric acid. They 

 grow freely in the soil and multiply with considerable 

 rapidity, the result being the formation of certain quanti- 

 ties of organic substance. They cause the carbon dioxide to 

 enter into combination, this gas being normally the only 

 source of their supply of carbon. They possess no chlorophyll 

 and consequently cannot utilise directly the radiant energy 

 of the sun. Their energy is apparently derived from the 

 oxidation of the nitrogenous compounds which they attack. 

 Nothing is known at present of the steps by which the 

 synthesis of the organic matter takes place. 



A process which at first appeared to involve a mechanism 

 resembling that of the chlorophyll apparatus was discovered 

 some years ago by Engelmann. Certain bacteria which 

 contain a purple pigment were found to possess the power 

 of photosynthesis. The pigment was thought to be allied 

 to chlorophyll and to possess the same power of absorbing 

 and utilising the radiant energy of light. Recent researches 



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