380 PHOTOSYNTHESIS 



synthetic energy." Thus, if both values are placed at 100 in Tropceoliim 

 majus, the following results are obtained for other plants : 



"Specific 

 Photosynthetic Number of 



Energy" Chloroplasts 



Tropaolum majus 100 100 



Phascohis multiHorus 72 64 



Ricinus communis 118.5 120 



HcUanthus anmius 124.5 122 



Although the results show a general direct proportionality there is little 

 doubt that other factors also control the photosynthetic rate. 



In the lower plants containing only one or a few chloroplasts these are 

 frequently quite large, while in the higher plants they are smaller and 

 do not show great variation in size. Of the 215 species examined by 

 Mobius '"^ 50 per cent had chloroplasts which measured 5 n and 75 per 

 cent 4-6 |.i. The size varied from 3-10 \i, but only very few species had 

 chloroplasts over 7 |x. 



The chloroplasts exhibit a variety of form. They are often compact 

 bodies ranging in form from spherical, ellipsoidal, lens and disk-shaped 

 to rough-edged plates. Kiister ' ' has also described chloroplasts of fluid 

 or ameboid consistency found in the orchids. The physical structure of 

 the chloroplasts is apparently variable. They have been described on 

 the one hand as perfectly homogeneous bodies and, on the other hand, 

 as possessing a granular or spongy appearance containing droplets of oil. 

 This granular appearance may be due to the accumulation of starch or 

 oil, formed by photosynthesis, and held as reserve food material. Meyer "^ 

 has developed the idea of the structure of the chloroplasts as consisting 

 of a porous colorless mass which is filled with droplets of an oil or lipoidal 

 substance, the grana, in which the pigments are dissolved. It has also 

 been suggested that the oil is a direct product of photosynthesis, while 

 some consider the oil as a degradation product of the chloroplasts.'^ The 

 ultramicroscopic observations of Price -° indicate that the chloroplasts are 

 slightly opaque, heterogeneous bodies of a gel structure. In some plants 

 crystals, supposedly of proteins, have been observed as inclusions in the 

 chloroplasts. Ullrich ^^ has also demonstrated that the chloroplast may 

 play an important role in protein synthesis in the leaf, though all of the 

 protein in the chloroplast can evidently not function as temporary reserve 

 food material. The composition of the chloroplasts is not definitely 

 known, though doubtless the colorless portion, the stroma, contains pro- 



'« Mobius, Ber. bot. Ges., 38, 224 (1920). 

 "Kiister, ibid., 29, 362 (1911). 



" Meyer, "Das Chlorophyllkorn in Chemischer, Morphologischer und Biologischer 

 Beziehung," Leipzig, 1883. Meyer, Ber. bot. Ges., 35, 658 (1917); 36, 235 (1918). 



'"Liebaldt, Zeit. Bot., 5, 65 (1913). Rothert, Bull. Acad. Sci. Cracovic. Class 

 Math. Nat. Sci., 1911, p. 189. Lepeschkin, Ber. bot. Ges., 28, 91 (1910); 29, 181 

 (1911). Ponomarew, ibid., 32, 483 (1914). 



'"Price. Ann. Bot., 28, 601 (1914). 



"Ullrich, Zeit. Bot., 16, 513 (1924). 



