1908.] The Cosmical Function of the Green Plant. 457 



point any further increase of intensity will be of no avail and the curve 

 must remain parallel to the abscissa. 



Of course, I do not pretend that the two values are strictly con- 

 cordant, but still I think that they are of the same order of magnitude. 

 At all events in this thin film of chlorophyll where an effect corre- 

 sponding to a very high temperature may be realised, the surrounding 

 space remaining cold, the molecules of the carbon dioxide must be in a 

 state most favourable for their dissociation, resembling very much that 

 furnished by St. Claire Deville's classical tube cliaud et froiil. 



These considerations on the extreme tenuity of the chlorophyll film 

 lead to other conclusions the importance of which cannot be exag- 

 gerated. For the first time we get an approximate idea of the state of 

 concentration of the colouring matter in the chloroplast. If we take 

 for a unit the concentration of a solution presenting in a sheet of 

 1 cm. the typical emerald-green colour and the characteristic absorp- 

 tion spectrum, we arrive at the somewhat unexpected result that the 

 concentration in the natural state in the chloroplast is about four 

 thousand times greater. Practically it is very near the solid state, and 

 the superficial colour is nearly black. Two very important conclusions 

 may be inferred from this fact. The first is an explanation of the 

 total absence or very small degree of fluorescence observed in the living 

 green organs. In a very elaborate paper Walter has amply proved that 

 the fluorescence decreases rapidly when the concentration increases. 

 If we take into consideration the state of concentration of chlorophyll 

 in the chloroplast, we may easily account for this absence of fluorescence 

 in the green organs, and at the same time we must admit that the 

 chemical process going on in the chlorophyll molecule must be more 

 energetic when the loss of energy due to fluorescence is at its 

 minimum. For it is a fact, that those chlorophyll solutions which 

 present the least fluorescence are most easily bleached on being exposed 

 to light. 



The second conclusion is perhaps of still greater importance. It has 

 been very often repeated that chlorophyll extracted from a living plant 

 loses its power of reducing carbon dioxide, and direct experiments are 

 brought forward in support, in which chlorophyll solutions were put 

 into contact with carbon dioxide and exposed to sunlight without any 

 effect. Now we may see that the results of all these experiments 

 cannot be looked upon as a proof, the conditions being utterly different 

 from those in the chloroplast. The case is just as if we were to 

 measure the absorption of light by lamp-black, and instead of using 

 a coating of pure lamp-black we used a mixture of one part of black 

 and 4000 parts of oxide of zinc. Chlorophyll, as we have seen, is 

 practically black, and if we call it green, it is somewhat in the same 

 sense in which we might call lamp-black brown, for in extremely thin 

 sheets it is of that colour. In the solutions employed till now the 



