20 



BOTANY 



PART I 



chloroplasts. This frequently occurs, for example, in the superficial 

 portions of potato tubers. The leucoplasts have, in many cells at 

 least, the special function of transforming sugar into grains of starch, 



which appear within them. 



(e) Chromoplasts. These give the 

 yellow and red colour to many parts of 

 plants, especially to flowers and fruits. 

 They arise from the colourless chromato- 

 phores of embryonic cells or from previously 

 formed chloroplasts. They may resemble 

 the chloroplasts in shape but are often 

 smaller, while their colour is yellow or 

 orange-red. This depends either on xantho- 

 phyll or carotin. The pigments are not 

 uniformly dissolved in the chromoplast 

 but form minute droplets (grana) in the 

 FIG. lo.-ceii from the epidermis of p i asma ti c substance (the stroma) ( 19 ). The 



Rhoeo discolor, n, Nucleus with . 11 .1 L* J'l 



its nucieoiusoo, and surrounded pigments, especially the carotin, readily 

 by the leucoplasts (i). Proto- crystallise out and the chromoplasts then 

 B^^to^ety^rotopk^ become needle-shaped, triangular, or rhombic 



which is not represented, lining in form (FigS. 11, 12). 



the wall, (x 240.) 



The origin and significance of the red EYE-SPOTS 



which are found in the cells of many Algae, especially in their motile cells, are 

 insufficient!}' known. The eye-spot occurs in the neighbourhood of the chloroplast 

 and is often connected with this (Fig. 333, 1 a). Some investigators hold that it 



FIG. 11. Cell from the upper surface of the 

 calyx of Tropaeolum majus, showing 

 chromoplasts. (x 540. After STRAS- 

 BURGER.) 



FIG. 12. Chromoplasts of the Carrot, some 

 with included starch grains, (x 540. 

 After STRASBUROER.) 



should be reckoned with the chloroplast and that it serves for the perception of 

 light somewhat as the eye does. The red pigment, which has been termed HAEMATO- 

 CHROME, is simply carotin. 



