pringsheim's researches on chlorophyll. 89 



chlorophyll-corpuscles, some or a single corpuscle may be 

 acted upon. 



But, besides destroying the colouring matter, the liglit 

 affects the cell-contents also, and especially those elements 

 concerned in respiration and nutrition. In Spirogyra, which, 

 in consequence of its organisation (with the nucleus em- 

 bedded in a central plasma from which threads radiate to 

 the periphery, and with a granular motion in the protoplasm 

 between the chlorophyll- bands) is very suitable for study, 

 either before or after complete decolorisation of the bands, 

 an extending destruction of the cell-contents is observed. 

 The motion of granules in the protoplasm of the cell-wall 

 ceases. The threads of protoplasm contract and pull thereby 

 the middle part of the coils of the chloro})hyll-bands deep 

 into the lumen of the cell, and at the same time a portion 

 of their substance withdraws to the central plasma-mass, 

 which swells into a large vesicle with a distinctly double- 

 contoured membrane of considerable thickness (fig. 11 h). 

 Then the threads rupture, and the proximal ends remain 

 as fragments attached to the central plasma, whilst the 

 distal portions adhere to the amylum-bodies. Whilst these 

 changes are progressing there appear u^on the threads 

 small, defined, vesicle-like formations (fig. 11a), which are 

 undoubtedly distinct morphological structures, and in the 

 normal uninsolated cell are occasionally seen, as before 

 mentioned, at the forks of the threads. These plasma-knots, 

 as they may be called, which are also to be seen in Sjnrogyra 

 cells killed by other means, are withdrawn with the substance 

 of the thread to the central plasma, and coat its surface, often 

 in great numbers (fig. 11 b). Through the contraction and 

 rupture of the threads the nucleus is pushed from its central 

 position and displaced to a greater or less extent (figs. 19), 

 always surrounded by the central plasma with its coating of 

 plasma-knots. It, along with the nucleoli, retains its form, 

 but sometimes, at least in one-spired species of Spirogyra, 

 appears to have lost portion of its substance, whilst in other 

 cases it becomes granular in aspect and acquires a red tinge. 

 The turgescence of the cell is markedly affected (in fig. 18, 

 between d and e, the partition wall bulges into the insolated 

 cell), and alterations in the substance of the layer of proto- 

 plasm lining the cell-wall, which are chiefly recognisable by 

 colour changes, occur. 



Many oi these effects in the protoplasm are familiar as 

 appearances connected with death of the cells from other 

 causes, e.g. from heat or mechanical injury ; but in such 

 cases the changes are not identical in their whole course 



