90 pringsheim's researches on chlorophyll. 



with those just desciibed. Here the effects are the result 

 of a definite photochemical action, and many of them are 

 specific of death from light, although they are combined 

 with the general changes in the protoplasm, which appear 

 after death from any cause. 



Effects similar to those seen in Spirogyra occur, with 

 niodifi.cation dependent upon organisation, in other Algce 

 with so-called formless chlorophyll-masses ; for example, in 

 Mesocarpus (fig. 20), (Edogoiiium, Draparnaldlay Vauche- 

 ria, Sec, always varying in extent, up to complete death 

 of the cell, according to the duration of exposure to light. 

 Also in cells with definite chlorophyll-corpuscles, such as 

 occur in Characece, Musci, ferns and phanerogams, like results 

 obtain. Amongst these, Characecs are most favourable for 

 investigation on account of the power of recovery of their 

 cells even after considerable injury, the structural relation- 

 ships of these, and especially their great length, which permits 

 of a small portion of one cell being insolated. 



If a portion "3 mm. in diameter, of a Nitella ceW, which is 

 about 1 mm. long, and not too thick, be insolated, it is more 

 or less completely decolorised in a few, usually three to eight, 

 minutes (figs. 31^ 32). Quite independently of the decolor- 

 isation, except in so far as the chlorophyll colouring matter 

 acts as a screen, the destruction of the cell-contents begins 

 and may extend until the whole content is killed. It is 

 possible, however, to regulate the action so that death of the 

 cell shall precede complete decolorisation of the insolated 

 area, or shall succeed it, or that the only effect shall be the 

 destruction of the colouring matter without injury to the life 

 of the cell. This depends, in the first instance, upon the 

 specific energy of the plant but also upon the depth and the 

 size of the cell. 



In deep plant cells, such as those of adult leaves, or the 

 internodal cells of Nitella, which are lined with a dense 

 persistent layer of chlorophyll-corpuscles, the depth of 

 the cell and the protection of the layer of chlorophyll- 

 corpuscles have great influence in modifying the action. 

 The cell in such a case lies with its lower, or an ideal 

 median, or its upper surface in the plane of most intense 

 illumination, and the parts above or below such plane must 

 be affected in a different degree. The layer of chlorophyll- 

 corpuscles on the lower surface of the cell will protect in 

 great measure the portions above so long as the chlorophyll 

 colouring matter is not destroyed, and in like manner the 

 centre of the layer of chlorophyll-corpuscles on the upper 

 wall of the cell will be sooner decolorised than the sides of 



