and the Function of Chlorophyll in Plants. 67 



other respects quite normally, remains living, and may even 

 continue to grow. 



This incapacity of the cell, and of every single chlorophyll- 

 grain, to regenerate the colouring-matter destroyed by light 

 holds good for all, even the least, degrees of weakening or de- 

 struction of colour in the chlorophyll-grain. It hence follows 

 that the destruction of chlorophyll by light cannot be a normal, 

 physiological act in the life of the plant, but is a detrimental 

 and pathological process. 



What becomes of the chlorophyll colouring-matter on its 

 destruction by light in the cell I could not make out, although 

 I took much pains for the purpose of doing so. I did not 

 succeed in a microchemical way in discovering any substance, 

 in the cell decolorized by light, which could be regarded as 

 the product of the destruction of the chlorophyll. A possible 

 simultaneous augmentation of the oil or the starch of the 

 decolorized cell, or the formation of grape-sugar or dextrine, 

 cannot be ascertained. Hence I am inclined, so far as my 

 investigations have yet extended, to assume that herein the 

 chlorophyll passes direct into the gaseous products of the 

 respiration of the plant. 



With respect to the rest of the above-sketched destruction- 

 phenomena, which occur with these experiments in intensified 

 light in the protoplasm and the not green contents of the cell, 

 and which can be heightened to the death of the cell, there is 

 no doubt that they too are direct photochemical actions of 

 light. They are not immediate thermal effects of the sun's 

 image ; nor are they secondary phenomena produced, as might 

 perhaps be thought, by some yet unknown poisonous products 

 of the destruction of the chlorophyll colouring-matter in light. 

 This is proved, first, by experiment on cells which are colour- 

 less and contain no chlorophyll — as, for example, on the hairs 

 of the filaments of Tradescantia, on the stinging-hairs of 

 Urtica, &c, in which the arrest of the motion in the threads 

 of protoplasm and their destruction in light occur in a similar 

 manner and under the same circumstances as in green cells 

 and is promoted by the presence of oxygen. 



A sufficiently rigorous demonstration can moreover be ob- 

 tained with green cells and tissues, if, in the way above men- 

 tioned, we shorten the duration of the experiment, breaking 

 it off after the destruction of the chlorophyll and before the 

 cell-contents beneath this have suffered under the action of 

 the light. Singularly favourable for experiments of this kind 

 are the long utricles of Nitella. If a small fraction of the 

 length of one of these be exposed to the influence of light, 

 and the experiment be stopped when the chlorophyll is de- 



5* 



