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 

 is called etiolin). Phaeophyll, the brown pigment 

 of the Phaeophyceae, is closely related to chloro- 

 phyll. Chlorophyll differs widely in tint. The 

 leaves of succulent plants, salt plants, and epiphytes 

 have a pale green color that is in strong contrast 

 to the dark green color of beech leaves and of 

 shade leaves generally. The deep green tints of 

 shade leaves may be due in part to the greater 

 concentration of the chlorophyllin, in part to the 

 paucity of xantho- 

 phyll, and in part to 

 the number and size 

 of the plastids. 



Miscellaneous features. Chloroplasts 

 contain various inclusions, notably starch 

 grains (fig. 756; alsofig-733); the pyrenoids 

 of algae and of Anthoceros are protein 

 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- 



FiG. 755. Cells from 

 a perianth segment of the 

 nasturtium (Tropaeolum)i 

 showing variations in 

 the form of chromoplasts, 

 some (c) resembling 

 chloroplasts in shape, 

 while others (m) are ir- 

 regular in outline; these 

 chromoplasts are yellow 

 or orange in color; in 

 addition there may be a 

 red pigment, anthocyan, 

 diffused in the cell sap 

 (position here indicated 

 by lines, a) ; highly mag- 

 nified. 



FIG. 756. Two chloroplasts 

 of Rhipsalis with several grains of 

 starch (s) and many minute oil 

 drops; highly magnified. From 

 SCHIMPER. 



