28 ORGANOaRAPHT. 



green colour, hence it is clear that thexconsist of a substance 

 which is coloured green by the presence of colouring matter 

 diffm?^ through them whfch Ts soIuBle in alcohol or__etlierr~The 

 granules when thus freed from green colouring matter are co- 

 loured 3'ellow by iodine, and therefore contain nitrogen. It 

 would seem probable from this, as well as from their common 

 occurrence around the starch granules (which, as we shall find 

 in speaking of starch, are developed from protoplasm), that they 

 are simply granules of protoplasm permeated by a green colour- 

 ing matter to which the name of chlorophyll is alone properly 

 applied. Chlorophyll consists of carbon, oxygen, hydrogen, and 

 nitrogen, but the proportion of these has not been accurately 

 ascertained. It appears to be of a resinous nature. According 

 to Fremy, chlorophyll is composed of two colouring principles, 

 ,one blue, called. 2)hj/Ilocj/ani7i, and the other yellow, termed _p%/- 

 loxanthin. C hlorophyll is only formed under the influence of 

 liffht : it never occurs tiierefore in structures removed from that 



agen *:, but exclusively on the plTrts of pl ants nea r the" s urface.^ 

 In the autumn it iindergoes certain changes which are not well 

 understood, by which it loses its green colour, and assumes 

 various shades of red or yellow. Fremy attributes the yellow 

 colour of fading autumnal leaves to the gradual destruction of 

 phyllocyani n. ' — 



All tne colouring matters contained in the cells which are not | 

 Fia 5'? green, and to which the peculiar tints of the petals 

 _' "' and other parts are due, are frequently comprised 

 under the common name of cliromuh . These are 

 of various natures, although, according to Fremy 

 and Cloez, all the colours assumed by flowers may 

 be referred -to three separate principles, one of 

 which is of a blue or rose colour, and is named 

 I c y anvil ; while the other two are yellow, and termed 

 -'^Yi" ■''p ^f" f* xanthin and xav thcin. 

 taiiiing starch- " Starch. — There is no substance contained in the 

 granules. cells which has given rise to more discussion as to 



its origin and nature than starch. It is, with the exception of 

 protoplasm, the most abundant and universally distributed of all 

 the cell-contents, occurring as it does, more or less, in all pa- 

 renchymatous cells {fig. 52), except those of the epidermis. It 

 is, however, most abundant in the matured structures of a plant, 

 as in the pith of stems, seeds, roots, and other internal and 

 subterranean organs which are removed from the influence of 

 I light. In these respects it presents a marked contrast to chlo- 

 I ryphyll, which occurs only in young and vitally active structures, 

 I which are placed near the surface of plants, and directly ex- 

 jt posed to light. When starch occurs in the active vegetating 

 I parts, it is then commonly invested by chlorophyll granules. 

 Starch is not only widely distributed through the different 



