232 



NUTRITIVE METABOLISM 



It will be necessary to renew the material in the jar containing 

 the pumice stone and potassium hydrate at least twice during the 

 test. 1 Test the composition of the atmosphere in the bell-jar at 



the close of the experi- 

 ment by the method de- 

 scribed in 302. 



298. Conditions Af- 

 fecting Photosynthesis. 

 It has been shown by 

 the preceding experiments that the 

 chief factors in the mechanism of 

 photosynthesis are light, chlorophyl, 

 and the presence of carbon dioxide in a 

 gaseous form. In addition it is to be said 

 that a chloroplast is unable to carry on this 

 process, until a certain stage of its forma- 

 tion has been reached, and also that if the 

 chlorophyl in a plastid, is bleached beyond 

 a certain point it may not be renewed and 

 the chloroplast is destroyed. The synthetic 

 process may be continued in arctic species 

 until the plant is actually frozen while in 

 others it is inhibited by a temperature 

 above the freezing point. The maximum 

 temperature is probably less than 50° C. in 

 all species, and inhibition ensues at tempera- 

 tures much below this in the greater major- 

 ity of plants. Both points are influenced 

 by the amount of atmospheric moisture. 

 Anaesthetics and all chemical agents which check the action of 

 protoplasm, exercise a retarding and inhibitory influence on the 

 process, while the accumulation of the products in the cells acts 

 in the same manner. It is probable that photosynthesis proceeds 



1 MacDougaL Relation of the growth of leaves and the- chlorophyl function. 

 Jour. Linn. Soc. 31 : 526. 1896. 



Fig. 115 Arisaema tri- 

 phyttum grown in an at- 

 mosphere free from car 

 bon dioxide. 



