PRINGSHEIm's researches on CHl.OllOPHYLL. 107 



it brings about in the substance of the protoplasm. As 

 soon as light has operated sufficiently long, one sees, e.g. in 

 Nitella, the movement slowing at the insolated spot, and 

 the streaming protoplasm in consequence aggregates in large, 

 often striated, masses about it. Then, especially if the cell 

 be long and the insolated area near its middle, as the cur- 

 rent cannot cross the insolated area, two currents frequently 

 arise in one cell, each following a course of its own, separated 

 from the other by the insolated part. 



These pheenomena are to be explained by the greater 

 immobility of the protoplasm which has been exposed to 

 light. Because protoplasm aggregates at the insolated area, 

 it does not necessarily follow that it is as it were drawn by 

 the light, but only that in certain intensities the motion 

 of the protoplasm is slowed at the insolated area. And so 

 also the opposite effect, the aggregauon of the protoplasm 

 at the shaded spots, is to be explained by the commencing 

 inmiobility of the insolated portion forcing the protoplasm 

 into other channels. The disposition of the moving masses 

 in the cell shows only the relative motility of the proto- 

 plasm in different, relatively darker and lighter, places cor- 

 responding with the oxidation of its substance as i'jfluenced 

 by light. 



4. The membrane of the cell in intense light. — The cell-wall 

 exhibits no very striking chatiges. At times, in more delicate 

 Spii'ogyra-ceWs a slight swelling may be seen. If, however, 

 delicate species of Spirogyra, e.g. Sp. Weberi or species of 

 31esocarpus, be exposed to light until death of the cells sets 

 in, the insolated cells separate more or less completely one 

 from another (figs. 20, 21), and in *S^. Weberi the infolded 

 ends of the cells unfold. The changes in turgescence of the in- 

 solated cells appear to have notliingto do with this appearance; 

 nor is any perceptible shortening or lengthening of the cell 

 walls apparent. But at the moment of separation a slight 

 torsion of the threads is observable, and possibly an inequality 

 in tension between the cuticle and the inner layers of the 

 membrane, developing under the influence of insolation, may 

 cause the torsion and consequent separation. It is possible, 

 however, that chemical changes of the membrane at the 

 limits of the cells may contribute to the resuh. 



IV. Respiration in Light of Green Tissues and the f miction 



of Chlorophxjll. 



All the forementioned results lead to the conclusion that 



the amount of oxygen inhalation exercises a very definite 



influence upou the assimilation by chlorophyll-corpuscles, 



