THE EFFECTS OF HEAT AND RADIANT ENERGY 115 



which, under the influence of light, falls apart in such a way as to yield 

 chlorophyll (or the catalyzer contained therein), O 2 , and a third prod- 

 uct, the latter being sugar or a substance from which sugar may be 

 formed. It is obvious that Hoppe-Seyler's idea represents that con- 

 ception of the action of the catalyzer which is more and more supported 

 by the facts. 



The different parts of the spectrum do not accelerate the process 

 of assimilation equally well; chlorophyll absorbs the rays between 

 B and C of the spectrum, and also the rays beyond F. Engelmann 

 has shown by a very ingenious method that the rays between B and C 

 cause the most vigorous assimilation, that the effectiveness of the rays 

 between D and E is a minimum, and that a second maximum exists 

 beyond F* Those rays are therefore the most effective for the pro- 

 cess of assimilation which are most vigorously absorbed by the 

 chlorophyll. 



It is as yet uncertain whether the light influences directly any other 

 synthetic processes than those which lead to the formation of sugars 

 and starch. f The lack of light must make itself felt in an indirect way 

 in any process in the plant for which the formation of carbohydrates 

 is a prerequisite, e.g. the formation of proteins. 



The life of animals does not depend so directly upon the presence 

 of light. This is evidenced by the fact that animal life occurs in caves. 

 Life at the bottom of the ocean also occurs practically in the dark, 

 inasmuch as the light furnished by phosphorescence is only slight. It 

 has occasionally been stated that eggs of animals develop better or 

 quicker in the light than in the dark; but a closer analysis of such 

 statements has shown invariably, thus far, that they are due to an 

 experimental error. Some authors managed by faulty methods to ex- 

 clude the air also with the light, and others did not exclude or consider 

 the influence of microorganisms in their experiments. Driesch's 

 experiments have failed to show any influence of light upon the develop- 

 ment of eggs; and my own experiments in that direction have also 

 thus far yielded only negative results. The fact that the eggs of mam- 

 mals develop in the uterus, shows sufficiently that eggs can develop in 

 the dark. 



In years of experimenting I have found only one form of animals 

 in which diffused daylight has an influence upon the formation of organs ; 

 namely, Eitdendrium, a hydroid.J When stems of Eudendrium are 



* Engelmann, Pfl tiger's Archiv, Vol. 27, p. 485, 1882 ; and Vol. 38, p. 386, 1886. 



t As fungi can form proteids in the dark when a carbohydrate is contained in the cul- 

 ture medium, it seems at least possible that light is not directly required for the formation of 

 proteids in green plants. 



1 Loeb, Pfliiger's Archiv, Vol. 63, p. 273, 1895. 



