PRINGSHEIM S RESEARCHES ON CHLOROPHYLL. 85 



the structural character of a hollow sponge or network, their 

 meshes are permeated by the hypochlorin and the oily 

 vehicle with the colouring matter, which can, by the methods 

 mentioned, be readily extracted. In the interior, too, of 

 these hollow perforate chlorophyll-corpuscles, the secondary 

 deposit of starch and such like formative material takes 

 place. The whole organisation of the chlorophyll-corpuscles 

 is thus admirably suited for the performance of their func- 

 tion, and they are peculiarly fitted for absorbing and con- 

 densing gases. 



II. On the Method of Microscopical Photochemistry. 



This method has been designed with the view of directly 

 observing under the microscope the action of light on the 

 contents of plant-cells, and of determining the light and heat 

 absorption in the several elements of the cells and the 

 activity stirred up within the tissue by the sun's rays. It is 

 complementary to and an extension of the analytical methods 

 hitherto employed for determining gas interchange in white 

 and in coloured light, and it permits of a more correct and 

 complete explanation of the experimentally-known facts of 

 the respiratory process in plants. For whilst the most 

 accurate quantitative and qualitative estimation of inspired 

 and expired gases gives no clue to the share which the indi- 

 vidual cell-elements take in the respiration, the observation 

 under the microscope of the action of light in the cells, in 

 circumstances wliich promote a rapid effect, enables the 

 changes taking place in the elements, as well as the condi- 

 tions under which they are, or are not, brought about, to be 

 carefully studied. 



A high light intensity is necessary to produce quickly the 

 desired effects. Experiments upon plants with intense light 

 are greatly required, espe(;ially with reference to tlie rela- 

 tive energy of the different rays of the spectrum in gas- 

 interchange. Plants growing behind coloured screens are 

 evidently in relative darkness, varying with the colour, as 

 compared with normal conditions, and as researches into 

 this subject have all been conducted after this method, the 

 results are only valid for low and insufficient intensities. 

 More particularly is this the case with the so-called chemi- 

 cal rays. These blue and violet rays are usually considered 

 as being active only in heliotropic phenomena, and as having 

 little or almost no effect in gas-interchange of plants. But all 

 coloured screens (blue glass and sufficiently concentrated solu- 

 tions of ammonia copper sulphate) used to produce monochro- 

 matic blue or violet light, are very dark. Tliey allow in diffuse 



