64 M. Pringsheim on the Action of Light 



minutely only into that part of my researches which has for 

 its subject the influence of light upon the plant-cell. 



If a chlorophyll-bearing tissue, or even a single cell con- 

 taining chlorophyll (a moss-leaf, a fern-prothallium, a Char a, 

 a Conferva, or a section of a leaf of any Phanerogamic water- 

 or land-plant &c), be placed in the usual manner under the 

 microscope, while, at the same time, by means of a heliostat 

 and a lens of about 60 millims. diameter, the image of the sun 

 is thrown upon the plane of the field of vision at the spot in 

 which the object is, so that the latter appears formally im- 

 mersed in the image, in a few minutes (from 3 to 6 and 

 upwards) very considerable and energetic changes can be seen 

 to take place in the object. 



The first phenomenon seen, more striking than any other, 

 is the complete destruction of the chlorophyll under the eye of 

 the observer. The green plant-cell, exposed only a few 

 minutes to the concentrated sunlight, makes exactly the same 

 impression as if it had lain for twenty-four hours in strong 

 alcohol. The green colouring-matter has disappeared, while 

 the primitive substance of the chlorophyll has for the most 

 part its forms entirely preserved, and even its nature appa- 

 rently not essentially altered. But in the experiments in the 

 light it will be possible to localize the decolorization, and at 

 pleasure to confine it to a single cell or even a portion of a 

 cell ; for the destruction strikes only the place upon which the 

 light is directly incident ; so that, for instance, in a cell a 

 single chlorophyll-grain, a single turn of a filament in a 

 Spirogyra, &c. are decolorized, while the adjacent grains of 

 chlorophyll and the next preceding and following coils remain 

 intact in form and colour. 



The changes which take place, however, are not limited to 

 the destruction of the green colouring-matter only ; they 

 gradually attack also the other constituents of the cell, and, 

 according to the duration of the action of the light, go on to 

 the complete death of the entire cell. Thus, if its duration 

 is protracted, the motion of the granules in threads of pro- 

 toplasm, and the circulation of the protoplasm itself, where 

 they previously existed (as in the utricles of Nitellm and 

 Charw, in the leaf-cells of Vallisneria, in the hairs of the 

 staminal filaments of Tradescantia, in the stinging hairs of 

 Urtica, &c.) , are arrested ; the threads of protoplasm break ; 

 the normal arrangement of the cell-contents is destroyed ; 

 the cytoblast, where it occupies certain positions (as in the 

 Spirogyrce), is dislocated, breaks away from the threads of 

 protoplasm to which it is suspended ; the cuticular layer con- 

 tracts, loses its impermeability to colouring-matters ; the 



