pringsheim's researches on chlorophyll. 91 



of the cell where many rows of chlorophyll-corpuscles lie 

 over one another. In Spirofft/ra like circumstances have to 

 be considered, but only in small degree even in the species 

 with deep cells, because of their small diameter, and also 

 because the lower flexures of the bands afford but a small 

 protection to the upper. Yet one finds that the points on the 

 upper flexures where the lower flexures cross them especially 

 at the edges of the cell-wall, and the spots where the bands 

 commence to bend on the lower surface of the cell are later in 

 being decolorised than the freely exposed and unprotected 

 parts. A simple unscreened layer of chlorophyll-corpuscles, 

 or a chlorophyll-plate, such as that of Mesocarpus, when it 

 lies in a plane at right angles to the light, is decolorised in 

 from one-and-a-half to two minutes. The layer on the 

 upper wall of a Nitella ceW requires in light of equal in- 

 tensity five to eight minutes of insolation. 



But the length of the cell modifies the destruction of the 

 cell-content when exposed to intense light. As the proto- 

 plasm in the cells of Nitella is in constant slow streaming 

 movement during examination, any one portion of the proto- 

 plasm is only subjected for a relatively short period to 

 direct insolation, dependent, indeed, upon the size of the 

 insolated area as compared with the size of the whole cell, 

 and thus the protoplasm is acted upon by the light inter- 

 ruptedly. Each portion of the protoplasm, as it rotates round 

 the sides of the non-illuminated part is protected from light, 

 and only again is acted on when it reaches the insolated area. 



In Nitella the destruction of the chlorophyll colouring 

 matter depends therefore mainly upon the depth of the 

 cells, whilst the destruction of the protoplasm is also 

 influenced by the length of the cell; so that the immediate 

 appearances in the local destruction of a Nitella cell may be 

 very different. 



If the cell be a long and strongly grown one the complete 

 decolorisation of the insolated part may occur without any trace 

 of further destruction of content. The chlorophyll-corpuscles 

 in the non-illuminated part remain normal in form, colour, 

 and disposition. The neutral zone persists, and there is no 

 retraction of the protoplasmic utricle from the cell-wall. 

 Rotation of the protoplasm and contained bodies shows, as 

 a rule, no visible disturbance ; there may, however, occa- 

 sionally be a momentary cessation of the movement. 



In other cells, and specially if the insolation of a lianted 

 area be rapid, death throughout the whole cell may occur long 

 before complete decolorisation of the insolated part, or even 

 before the chlorophyll-corpuscles in this position show much 



