DIV. i MORPHOLOGY 19 



XANTHOPHYLL (oxide of carotin, C^H^O^}. Only the chlorophylls are concerned 

 in the assimilation of carbon dioxide. 



All four pigments can be extracted from the fresh or dried chloroplasts by 

 various solvents, e.g. by acetone or 80-90 % alcohol. . A deep-coloured solution 

 containing all the pigments can be most readily obtained by pouring boiling alcohol 

 on fresh leaves. Owing to the contained chlorophyll such a solution is deep green 

 by transmitted light, but blood-red, owing to FLUORESCENCE, by reflected light. 

 Its spectrum (Fig. 248) is characterised by four absorption bands in the less refractive 

 portion and three in the more refractive half. The individual pigments can be 

 separated by shaking the solution with various solvents. Thus benzol extracts 

 the chlorophyll and accumulates as a green solution above the alcoholic solution 

 which is now yellow. The amount of chlorophyll present in green parts of plants 

 is relatively small, amounting, according to WILLSTATTER, to O'5-l'O % of the dry 

 substance. 



The variegated forms of some cultivated plants have larger or smaller areas of 

 the leaf of a white or golden colour. The cells here contain colourless or yellow 

 chromatophores instead of the green chloroplasts. 



Many Algae are not green but exhibit other colours. In the blue - green, 

 verdigris-green, blue, or less commonly violet-coloured Cyauophyceae, and in the red, 

 violet, or reddish-brown chloroplasts of the Rhodophyceae, there are, in addition to 

 the four pigments of the green chloroplasts, a blue pigment called PHYCOCYAN, and 

 a red pigment, PHYCOERYTHRIN. These may occur singly or together, and both 

 are readily dissolved from the dead cells by water containing a little alkali or 

 neutral salt and yield a beautifully fluorescent solution. The phycocyan may often 

 be found as a blue border surrounding one of the Cyanophyceae dried upon paper. 

 Both pigments appear to be of proteid nature. Little is known as to their 

 significance ( 16 ). In the Brown Algae the colour of the brown or yellow chloroplasts 

 is due to their containing, in addition to chlorophyll a and a little chlorophyll b, 

 carotin and xanthophyll, the reddish-brown FUCOXANTHIN (C^H^Og), which is 

 allied to the last-named pigment ( 17 ). 



The colourings ( 18 ) which the leaves of trees assume in autumn before they fall 

 are connected with a breaking down of the chloroplasts and then* pigments. There 

 remain in the protoplasts, in addition to a watery and often reddish-coloured fluid, 

 only some oil-drops, crystals, and yellow highly refractive spheres. The case is 

 different in those Coniferae whose leaves turn brown in winter and again become 

 green in the spring ; the changes undergone by the pigments in the chloroplasts 

 are here reversible. The assumption of a brown colour by dying foliage-leaves is a 

 post mortem phenomenon in which brown pigments soluble in water are produced. 



In some phanerogamic parasites the chloroplasts are replaced by 

 colourless, brownish, or reddish chromatophores, which may, however, 

 in some of these plants still contain a trace of chlorophyll. In the 

 Fungi chromatophores are completely wanting, as has already been 

 mentioned. 



(b) Leucoplasts. In the interior of plants, where light cannot 

 penetrate, leucoplasts are developed from the rudiments of the 

 chromatophores instead of chloroplasts. They are usually of minute 

 size (Figs. 5, 10 /), mostly spherical in shape, but often somewhat 

 elongated in consequence of enclosed albuminous crystals (Fig. 28 AT). 

 If the leucoplasts become exposed .to the light, they may change into 



