December 12, 1902.] 



SCIENCE. 



927 



chloroplast, with the formation of carbon 

 monoxide and oxygen. Pfeffer has sug- 

 gested that perhaps the decomposition of 

 the gas is not due to the light rays at all, 

 and that they may exercise only a stimula- 

 ting influence upon the chloroplast, the 

 energy concerned being derived from heat 

 rays directly absorbed, or heat vibrations 

 derived from the more rapidly vibrating 

 light rays. In this case is the decomposi- 

 tion brought about directly by the heat 

 vibrations, or have we a transmutation into 

 some other form of energy? The whole 

 subject seems at all events a promising sub- 

 ject for inquiry. 



Another problem connected with the ac- 

 tion of chlorophyll is associated with the 

 absorption of radiant energy by the differ- 

 ent regions of the spectrum. Bands of 

 considerable intensity are noticeable in the 

 blue and violet, though the deepest absorp- 

 tion takes place in the red. Yet Engel- 

 mann's classic bacterium method shows us 

 that very little evolution of oxygen takes 

 place in the position of these bands in the 

 blue and violet. The fact that absorption 

 of radiant energy and photosynthetic ac- 

 tivity show no quantitative relationship is 

 of course not new, but the reason remains 

 still to be discovered. Van Tieghem has 

 suggested an explanation which recalls to 

 us the hypothesis advanced by Pfeffer, just 

 alluded to. This explanation is that there 

 are two factors concerned in the action of 

 chlorophyll, the elective absorption of light, 

 shown by the occurrence of the absorption 

 bands in the spectrum, and the calorific 

 energy of the absorbed radiations. The 

 failure of the rays of the blue and violet 

 to effect photosynthesis, in spite of their 

 absorption, would on this view be attribu- 

 table to their possessing but little calorific 

 energy. The latter is associated much more 

 strongly with the deep band in the red, 

 which is the seat of the maximum evolution 

 of oxygen when the spectrum is thrown 



upon a collection of active chloroplasts. 

 The heating rays alone are ineffectual, as 

 shown by the fact that there is no libera- 

 tion of oxygen in the region of the infra- 

 red, due no doubt to the fact that chloro- 

 phyll does not absorb these rays. 



Timiriazeff, in his classical researches on 

 the liberation of oxygen by the leaves of 

 the bamboo when exposed in tubes of small 

 caliber to a large spectrum, found that the 

 amount of carbon dioxide decomposed by 

 leaves is proportional to the distribution 

 of effective calorific energy in the spectrum. 



Van Tieghem 's hypothesis that this is a 

 matter of calorific energy may prove to be 

 erroneous, and yet his views may rest on 

 some sound basis. It may be a matter in 

 which electrical rather than calorific energy 

 may be concerned. 



Returning now to the chemical steps de- 

 manded by Baeyers's hypothesis, there are 

 certain considerations which may be urged 

 in favor of the view that carbon monoxide 

 really occurs in photosynthesis. It has 

 been ascertained by Norman Collie that 

 when a mixture of gases containing a large 

 proportion of carbon dioxide is exposed at 

 low pressures in a vacuum tube to the ac- 

 tion of an electric discharge from an in- 

 duction coil there is a very large formation 

 of the monoxide, together with oxygen, in 

 some cases as much as seventy per cent, of 

 the gas undergoing decomposition. 



Appealing to the experience of various 

 observers, there seems on the whole to be 

 a balance of evidence in favor of the power 

 of plants to live and prosper in an atmos- 

 phere containing a very considereable per- 

 centage of carbon monoxide. 



The question of the possibility of the lat- 

 ter replacing the dioxide, as the theory 

 appears to require, is complicated very 

 seriously by the differences of solubility 

 between them. Carbon dioxide dissolves 

 very readily in water and in cell sap ; car- 

 bon monoxide is almost insoluble in either. 



