558 



NATURE 



[April 15, 1SS0 



is possible that vegetable fats may be more propitious, or 

 that some other solvents may be found more closely 

 resembling the natural solvent of the chlorophyll-corpuscle 

 than those at present known. 



Apart, however, from the absence of sufficient evidence 

 to warrant the assumption that chlorophyll has a specifi: 

 chemical action on carbonic acid in the presence of sun- 

 light, there have to be considered (1) facts connected 

 with the part played by the sunlight which render it 

 improbable that chlorophyll is thus concerned, and (2) 

 facts which point to another use for chlorophyll, and one 

 which involves that concomitance of chlorophyll with 

 CO... decomposition which has been most strongly urged 

 in favour oF its supposed special property; (3) facts 

 which suggest that such chemical activity as that sorae- 

 ributed to chlorophyll is the special property of 

 protoplasm, or rather of the higher members of that 

 ever-asi descending scries of albuminoid 



bodies occurring in organisms, of which series the theo- 

 retical apex is entitled to the name "protoplasm" (so far 

 as the term can receive a chemical limitation). 



1. If chlorophyll were the active agent in C0 2 decom- 

 position under the influence of sunlight, we should expect 

 the r iy s ab .orbed by chlorophyll to be those most efficient 

 in promoting such decomposition. Such, it has been 

 shown by Sachs and others, is not the case. Light which 

 has traversed a solution of chlorophyll is still efficient in 



lie plant-cell (whatever part of the cell may be 

 called into play) to the decomposition of CO» and libera- 

 tion of O It i, true that the activity of light thus treated 

 is diminished, but that is explained by the fact that the 

 rays of the whole visible spectrum are some more, some 

 lcs-. capable of exciting the decomposition, and that the 

 total amount of light transmitted is much diminished. 

 The naxi mini evolution of oxygen by green plants is not 

 in the rei rays where chlorophyll most absorbs, nor in 

 the indig > and violet which it also largely absorbs, but in 

 thi low, the orange, and the green, which it allows to 

 pass entireh ex-ept for three very narrow and feeble 

 absorption binds. 



2. The 1 :tion of light on the chemical motion of proto- 

 pla-m 'an 1 we know of no changes in protoplasm which 

 can be considered as other than chemical) is known to 

 be ;i ver important one. Supposing that chlorophyll 

 is nut lirectly related to the action of light in exciting 

 the ■ nposition of carbonic acid by the true living 



re n plants, there are yet other activities of 

 of the plant-cell to which it may be related. 

 ;n inn has recently shown that luminous rays (inde- 



i of the obscure heat-rays) cause sudden con- 



trac n •> pr itoplasmic organisms devoid of chlorophyll 

 or < r pigment, whilst the expansion of yEthalium 

 or 1 ace of tan in the dark, and its contraction 



ben 1 the tan during sunlight, is a well-known 

 phe. tenon capable of experimental demonstration. 

 The iction of sol ir rays other than those highly endowed 

 property of exciting thermal vibrations upon the 

 livii ti sues of boih animals and plants appears to be 

 11101 ; ik 1 1, than has been usually admitted, 1 and due 



1 sun-burn'* produced by the glare of the electric light 



Vll!l sensation of heat, related both by Prof. Tyndal 



n Loclcyer, are in point. Further also the remarkable 



light on the phosphorescence of Beroe, as recorded 



by Pn Ulnun, Proe. Roy. Soc. Edinburgh, 1862. 



to a direct influence upon the protoplasm of living cells. 

 This being the case, it is not surprising that, supposing 

 the active agent in the decomposition of carbonic acid 

 in green plants to be the protoplasm itself, that activity 

 should be excited by the same part of the spectrum which 

 excites the human retina. At the same time it would not 

 be surprising that other specific chemical activities should 

 be promoted in protoplasm by the incidence of luminous 

 rays, and it may well be that chlorophyll has a relation 

 to these activities rather than to the decomposition ot 

 carbonic acid. 



It is here that the important suggestion of Prof. 

 Pringsheim (see Nature, vol xx. p. 86), based on 

 very simple but careful observations, comes in. The 

 respiration of the plant-cell is promoted according to 

 these observations by the action of light. Intense sun- 

 light in the presence of oxygen gas causes the chlorophyll 

 of a plant-cell (as watched with the microscope), to 

 oxidise and disappear. Similarly it causes decom] 

 and disruption of the protoplasmic portion of the cell. 

 Ultra-red rays have not this effect, and extreme red rays 

 have it but feebly, whilst the more refrangible rays, even 

 to an extreme distance [in the blue, exhibit it powerfully. 

 Here then is a chemical action taking place in the 

 plant-cell under the influence of light, and in tl 

 the rays which are active appear to be more nearly 

 coincident with those absorbed by chlorophyll than in the 

 case of C0 2 decomposition. It does not appear that the 

 oxidising process is non-existent in the absence of light, 

 but merely that it is far more active in the presence ot 

 light. Accordingly Prof. Pringsheim suggests that the 

 true function of chlorophyll is, by its general absorbent 

 action on light, to protect the'protoplasm of the cell from 

 this excessive oxidation, and especially to protect the 

 protoplasm of the chlorophyll corpuscles. Oxidation 

 being thus entirely or nearly entirely arrested in the 

 chlorophyll corpuscles, whilst proceeding in a lessened 

 degree in the general protoplasm of the cell, the proto- 

 plasm of the chlorophyll corpuscles is at liberty under the 

 influence of those rays of light which arc allowed to /'ass 

 by the chlorophyll (the very reverse of former supposi- 

 tions on the subject) to decompose carbonic aeid and 

 synthesise the elements of starch (or of hypochlorin). 

 And we know, as stated above, that the rays of light 

 allowed to pass by chlorophyll are those which are the 

 most efficient in the excitation of this activity. 



Prof. Pringsheim's hypothesis thus reconciles in a most 

 ingenious manner the concomitance of chlorophyll and 

 COo-decomposition with the inactivity of that body as 

 isolated and the apparent irrationality of its absorption- 

 phenomena. 



3. That so special an activity as the decomposition of 

 carbonic acid and synthesis of the elements of starch is 

 due to protoplasm itself and not to a body which, like 

 chlorophyll, appears to be of a comparatively simple 

 chemical nature, is probable on a priori grounds. 



Throughout the organic world — so far as our knowledge 

 goes, and it may be admitted that it does not go very far — 

 the more complex chemical processes connected with 

 nutrition on the one hand,, and secretion on the other 

 appear to be carried on directly under the influence of the 

 living substance of cells. We know of no formed-pro- 

 ducts similar to chlorophyll which stand between the gland- 



