NUMBER, SIZE, AND SHAPE 



357 



A characteristic feature of the chromoplasts of most algae are the 

 so-called pyrenoids, irregular-shaped bodies which are supposed to consist 

 of reserve proteins and are often surrounded by a starch sheath (cf. 

 Fig. 37a, b, c. According to Bose (1943) the oil droplets produced by 

 photosynthesis in algae first appear in these sheaths. 



The chloroplasts of the higher plants are contained mainl}^ in the 

 palisade and sponge tissues of the leaves (Fig. 38), and are quite uniform 

 in size and shape. They are discs or flat ellipsoids, 3-10 ix across. 

 Mobius (1920) measured hundreds of them, in many different species, 

 and found 5 ju as the most common size. Meyer (1912) measured the 

 three axes of numerous chloroplasts of Tropaeolum majus and found: the 



poUsode ) 

 ce/fs \ 



spongy 

 cells 



epidermis 

 sc/erenc^ma 



■scferenchyma 



aivmafe 

 fuard eel/ 



Fig. 38. — Chloroplasts in a leaf (from Meyer and Anderson 1939). Cross 

 section of a leaf of the tulip tree (Liriodendron tulipifera). (Courtesy of D. Van 

 Nostrand Company, Inc.) 



major axis from 3.0-4.9 n (average 3.9 n) ; the medium axis from 2.3-4.0 n 

 (average 2.9 n); the minor axis from 1.3-2.3 /x (average 1.6 /z); and the 

 volume (assuming an ellipsoidal shape) an average of 9.4 /x*. According 

 to Godnev and Kalishevich (1940), the average dimensions of the chloro- 

 plasts of Mnium are 6.4 X 5.4 /z; the average surface, 28 m" and the aver- 

 age volume, 41 n^. 



The number of chloroplasts in a single cell varies, in the higher 

 plants, from a few to a hundred or more. Haberlandt (1882) found an 

 average of 36 chloroplasts in each palisade cell, and 20 in each spongy 

 parenchyma cell of Ricinus communis, while Godnev and Kalishevich 

 (1940) counted an average of 106 chloroplasts per cell in over 7000 cells 

 in a leaf of Mnium. According to Haberlandt, the average number of 

 chloroplasts per cm.- of leaf surface, in six species, was between 3 and 



