790 REPORT— 1902. 



absorption fakes place in the red. Yet Engelmann'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 activity show no quantitative relationship is of course not new, but 

 the reason remains still to be discovered. Van Tieghem has suggested an e.xplana- 

 tion which recalls to us the hypothesis advanced by Pfetl'er, j ust alluded to. Thi^s 

 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 band.? 

 in the spectrum, and the calorific energy of the absorbed radiations. The failure 

 of the rays of the blue and violet to ettect photosynthesis, in spite of their absorp- 

 tion, would on this view be attributable to their possessing but little caloritie 

 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 liberation of oxygen in the region 

 of the infra-red, due no doubt to the fact that chlorophyll does not absorb these 

 rays. 



TimiriazefT, in his classical researches on the liberation of oxygen by the leaves 

 of tlie bamboo when exposed in tubes of small calibre to a large spectrum, found 

 that the amount of carbon dioxide decomposed by leaves is proportional to the 

 distribution of eflective 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 demanded by Baeyer's hypothesis there 

 are certain considerations which may be urged in favour of the view that carbon 

 monoxide really occurs in photosynthesis. It has been ascertained by Normaa 

 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 action of an electric 

 discharge from an induction coil there is a very large formation of the monoxide, 

 together with oxygen, in some cases as much as 70 per cent, of the gas, under- 

 going decomposition. 



Appealing to the experience of various observers there seems on the whole to 

 be a balance of evidence in favour of the power of plants to live and prospejr 

 in an atmosphere containing a very considerable percentage of carbon monoxide. 



The question of the possibility of the latter replacing the dioxide, as the 

 theorj' appears to require, is complicated very .'eriously by the diflerences of 

 solubility between them. Carbon dioxide dissolves very readily in water and in 

 cell sap ; carbon monoxide is almost insoluble in either. As the amount of a gas 

 taken up by a sohent depends not only on its solubility, but upon its partial 

 pressure, it is very e\ident that we cannot compare the two gases by admitting 

 the same quantity of both to plants under simultaneous comparison. It is only 

 necessary to supply the dioxide in the proportion of four parts in 10,000 ; but tlie 

 almost insoluble nature of the monoxide makes it inevitable that from tw^o to five 

 per cent, shall be experimented with. The same question of solubility makes it 

 almost out of the question to experiment with an aquatic plant. 



It would be of considerable interest from this point of view also to inquire 

 •whether if carbon monoxide is liberated at the outset of the photosynthetic pro- 

 cesses its combination with other groupings can take place apart from the actios 

 of chlorophyll. If so the fungi thould be capable of carbohydrate construction 

 if supplied under proper conditions with the monoxide and with hydrogen. The 

 proper conditions, however, might be extremely difiicult to establish. 



The next stage in the constructive processs aflbrds still ample room for 

 investigation. The presence of formaldehyde is not the hypothesis of Baeyer 

 alone, but is demanded according to Bach's views, though the stages of its hypo- 

 thetical construction are not the same. AVe have therefore to ask whether form- 

 aldehyde can be detected in plants, and if so whether the conditions under which it 

 may exist admit of its being considered an up-grade product in photosynthesis. 

 Objections to the theory of its formation may be advanced based upon its un- 



