522 



ECOLOGY 



In Anthoceros and Selaginella the chloroplasts in some cells are many 

 and small, while in other cells they are few and large (fig. 754). Sun 

 plants commonly have smaller chloroplasts than do shade and water 

 plants. The so-called chromoplasts of carrot 

 roots, nasturtium flowers, etc., often are irregular 

 in shape (fig. 755). 



The pigments. Chlorophyll is not a simple 

 green pigment, but it contains, in addition to the 

 green pigment or chlorophyllin, a yellow pigment 

 known as xanthophyll and an orange pigment 

 known as carotin. Closely related to xanthophyll 

 and carotin are most yellow, orange, and brown 

 pigments associated with color-bearing bodies 

 (chromatophores or plastids), including those of 

 yellow flowers, diatoms, and plants exposed to 

 darkness (i.e. etiolated plants, whose pigment often 



a p^ht^^ofto is called etiolin ^ Ph P h y 11 ' the brown Pigment 

 nasturtium (Tropaeolum}* of the Phaeophyceae, is closely related to chloro- 

 phyll. Chlorophyll differs widely in tint. The 



some (0 resembling leaves of succulent plants, salt plants, and epiphytes 

 chloroplasts in shape, have a pale green color that is in strong contrast 

 while others () are ir- to tne dark green color of beech leaves and of 



regular in outline; these 111 n rmj - . c 



chromoplasts are yellow shade leaves generally. The deep green tints of 

 or orange in color; in shade leaves may be due in part to the greater 

 addition there may be a concentration of the chlorophyllin, in part to the 



red pigment, anthocyan, . - , 



diffused in the cell sap P aUClt y f . Xanth - 

 (position here indicated phyll, and in part to 



the number and size 

 of the plastids. 

 Miscellaneous features. Chloroplasts FlG 7s6 . _ Two ch ] r 0p ia s ts 



contain various inclusions, notably Starch of Rhipsalis with several grains of 



grains (fig. 756; also fig.733); the pyrenoids starch ( J ) and man y minute oil 

 . , . . . drops; highly magnified. From 



of algae and of Anthoceros are protein SCHIMPER 



inclusions, and oil is common, especially 



in dying plastids. Plastids arise by division from preexisting plastids 



(fig. 753), and perhaps at times de novo in the cell cytoplasm, though 



careful search usually reveals them, even where their absence might be 



expected (e.g. in embryos). Although chlorophyll usually occurs only 



in chloroplasts, spectroscopic tests show its presence in the blue- 



showing variations in 

 the form of chromoplasts, 



by lines, a) ; highly mag- 

 nified. 



