pringsheim's researches on chlorophyll. 93 



game way, and paralysis and death niay be produced (fig. 

 27). Paralysis may occur before or after destruction of the 

 blue colouring matter of the cell-sap, and the circulation, 

 which is temporarily suspended, may after a longer or shorter 

 time return without the cell having suffered at all. Death 

 occurs in them also before complete destruction of the colour- 

 ing matter. Whenever the colour changes to violet the 

 protoplasm is killed, circulation is stopped and never returns, 

 and the protoplasm threads become granular,in ]mrtdisappear 

 or rupture irregularly, and the protopla-smic utricle, separating 

 from the cell-vv'all, collapses. A slight separation of the 

 cuticle over the insolated area is sometimes seen. 



B. Conditions of Light Action in Cells. — The effects 

 just described are dependent not only on the high intensity 

 of the light, but also upon its colour and the affinity for 

 oxygen of the cell-contents. All of them are produced 

 rapidly and energetically in white light. In coloured light, 

 on the other hand, there is not only a marked retardation 

 in rapidity of their appearance, but in red the light effect 

 is suppressed, although in dark green and blue the changes 

 are completed in a few minutes. The decolorisation 

 and death of the cells, which in white light are brought 

 about in two or three minutes, are accomplished in about 

 five minutes in green and blue light (Section vii, Exp. 

 1st Series). All these researches show that in any yellovv, 

 green, or blue light it is easy to decolorise and kill the cells 

 of many Alga, Characece, Musci, Filices, and Phanerogamce, 

 provided the colour eniployed is not too dark; whilst in red 

 light of the same intensity, and after twice or four times as 

 long exposure, no changes take place, and the red rays there- 

 fore appear to be protochemically inactive, or at least only 

 very slightly active, on plant-cells. 



That these effects are not due to the heat, considerable as 

 it must be in some coloured lights, generated at the focal 

 point of the large lens used, is evident from a comparison of 

 the changes accompanying death in cells from heat with 

 those here described. Tlie destruction of the colouring 

 matter will not be confounded in the two cases, but the 

 changes in the protoplasm, the paralysis and actual death of 

 the cells are alike, though not identical, from both causes. 

 This subject requires, therefore, further notice. 



In the first })lace, then, the temperature of the drop of 

 water in which the plants are examined does not rise suffi- 

 ciently high to cause the destructive action in the cells. 

 That this is the case may be assumed from the slow evapo- 



