PRINGSHEIm's tlKSEAKCHES ON CHLOROPHYLL. 105 



aniline-blue, the insolated cells become rapidly coloured^ the 

 iion-insolated are, even after some days, still uncoloured. 

 Nitella is very favourable tor such an observation, as the 

 differences, owing to the length of the cells, may be observed 

 in one and the same cell, and moreover, as the rotation is 

 not stopped, one may study the difference in permeability 

 between the cell-wall and the protoj)lasm, the former becom- 

 ing rapidly coloured, whilst beneath it the rotating proto- 

 plasm remains for a time unchanged. 



The greater permeability after insolfition is associated with 

 a distinct change in structure and in mass of the protoplasm 

 lining the cell-wall. It loses, hs has been shown, a con- 

 siderable amount of its contractile power. The ad<lition of 

 ])lasmolytic agents, such as iodine in iodide of potassium, 

 causes little or no retraction of the utricle in an inso- 

 lated cell (fig. 19), and it depends upon the intensity and 

 duration of exj)osure to light, as well as upon the thick- 

 ness of the lajer of protoplasm, to what extent the power of 

 contraction is lost. In Nitella this may be well studied. 

 Here, as has been already described, the contraction conse- 

 quent upon death from insolation advances gradually over 

 those portions of the cell which have not been insolated and 

 are green, the protoplasm at first slowly separating from the 

 cell-wall, and then subsequently collapsing. Only at the 

 insolated ])art does the utricle show no, or almost no, con- 

 traction, and mav be found with embedded skeletons of chlo- 

 rophyll-corpuscles still lining the cell-wall months after in- 

 solation (fig. 24). The reason for this is a partial destruction 

 of the protoplasm, which is the immediate effect of the light, 

 and as light only acts in presence of oxygen it is clear that 

 the oxygen must combine with certain elements of the 

 protoplasm of the utricle, and, as a result of the combustion, 

 that change and diminution of its substance occurs which 

 produces a loss of contractility. 



This loss of substance by oxidation in light may at times 

 be made directly visible. If a filament of Spirocjyra (one- 

 spired species are most suitable, as in them the utricle is not 

 strongly developed), some cells of which have \>qq\\ insolated, 

 be treated with a reagent which stains protoplasm deeply 

 (iodine solutions, for example), a more or less striking diffei'- 

 ence is observed between the contracted protoplasm of the 

 insolated and' the non-insolated cells. In the non-insolated 

 cells the former lining protoplasm of the wall no longer 

 forms a continuous uniform layer or plasma-utricle,^ but 



' Demonstrated by Printrsheim in 1854, in 'Untersuchungen iiber deu 

 Bau und die Bildung der Pilanzenzelle,' p. 10. 



