CONTENTS OF CELLS. 499 



usually solid and homogeneous when young ; subsequently they 

 often contain starch-granules in the interior, and not unfrequently 

 they become vacuolated like protoplasm when exposed to the direct 

 action of water. 



Fremy states that the green colour of chlorophyll is due to an 

 admixture of two substances, one yellow and the other blue, called 

 respectively phylloxanth ine tmd phyttocyanine ; but others think that 

 the blue substance is a modification of the yellow, brought about 

 by the agency of the acids. Our chemical knowledge of chloro- 

 phyll, however, is at present incomplete. Sorby states that chlo- 

 rophyll exists in a blue and in a yellow state. Blue chlorophyll 

 when dissolved in alcohol, is of a splendid blue-green colour, the 

 whole of the green part of the spectrum and part of the blue 

 being readily transmitted. Yellow chlorophyll absorbs the whole 

 of the blue and the blue end of the green, so that the colour is a 

 bright yellow-green. Chlorofucine is of a clear yellow-green, colour, 

 fluorescent like the two preceding. These three varieties of chloro- 

 phyll are insoluble in water, soluble in absolute alcohol, but not 

 always in carbon-bisulphide. Other colouring-matters, with different 

 optical properties and soluble in carbon bisulphide, are described 

 by Sorby. 



The chlorophyll-corpuscles are probably formed from the protoplasm 

 of the cell breaking up into distinct globular corpuscles, or distributing 

 itself according to patterns, as above indicated, upon the cell-wall. When 

 newly formed, in young cells, they are almost colourless, and appear in 

 the vicinity of the nucleus and in the layers or streaks of protoplasm ; and 

 we not unfrequently meet with protoplasmic corpuscles which differ from 

 chlorophyll -corpuscles only in the absence of the green colour. 



Development of Chlorophyll. The development of chlorophyll takes 

 place thus : In the young cell the protoplasm is colourless and disposed 

 in a thick layer around the inner wall of the cell ; in this appears first a 

 yellow colouring-matter ; and then the inner portion of this protoplasm 

 gradually splits up into polygonal portions, eacn of which becomes a grain 

 of chlorophyll. In other cases the chlorophyll is formed in a layer of pro- 

 toplasm surrounding the nucleus. Vacuoles are formed in it, and break up 

 the substance of the protoplasm into granules. In this latter case more 

 uncoloured protoplasm is left after the formation of the chlorophyll than 

 in the preceding case. 



Decay of Chlorophyll. The destruction or decay of chlorophyll shows 

 itself first in the change of colour from green to yellow or orange, or, in 

 the case of the spores of Algae, to red. This red colour is supposed to be due 

 to oxidation, assumed at the time when the spores come to rest ; when 

 active vegetation again commences, the green colour is restored. In the 

 case of leaves at the fall, the grains of chlorophyll diminish, then disappear 

 and give place to highly refracting granules of an orange colour, which 

 are the remnants of the disorganized chlorophyll, and to which the colour 

 of leaves in autumn is due (see p. 540). While these processes are going on, 



2x 2 

 I 



