Vcgetahle Fhysiolofjy. 



391 



or " leaf-green," as it is sometimes termed. It is well known that 

 the characteristic green colour of vegetation depends upon the 

 presence of this substance ; further, that its production is entirely 

 dependent upon the action of sun-light on the contents of cells, 

 and that its formation under this influence is directly connected 

 with the evolution of free oxygen, the result of a decomposition 

 of the very highest importance in the nutrition of plants. 

 Although, however, it has been experimentally ascertained that 

 the formation of the green colouring matter takes place in conse- 

 quence of an action of the sun's light, and that the quantity in a 

 given plant is as a rule proportionate to the amount of this 

 action, great obscurity prevails when we attempt to go below the 

 surface of these general statements. Moreover, although we see 

 every day that the formation of the solid structure of plants, and 

 of the more highly elaborated products rich in carbon, bears a 

 relation to the activity of the chlorophyll-forming process, it 

 is at present quite unsettled what that decomposition is which 

 gives rise to the foi'mation of the green colouring matter. Added 



Fig. 9. 



Cells from tlie muldle substance of the loaf of a grass {Poa) : a, in a natural state, the chlorophyll- 

 granules imneilded on the outside in the layer of protoplasm lining the wall of tlie cell ; b, a cell 

 with the " primordial utricle " contracted, bringing away the chlorophyll-granules from the cell- 

 wall; c, cell in which the green colouring matter has been extracted from ihe chlorophyll- 

 granules by alcohol ; d, similar cells with the "primordial utricle" contracted by tincture of 

 iodine; e, cell treated with a solution of potash, converting the whole contents into a green 

 gratmUr viscid mass contracted from the cell-wall, but hollow internally ; /, a cell treated with 

 acetic acid, the contents entirely converted into an olive-coloured fluid containing minute point- 

 liUe granules. Magnified 4U0 diameters. 



2 d2 



