310 PIGMENTS 



On the other hand, other investigators hold that the 

 chloroplasts may arise from differentiated parts of the proto- 

 plasm, which parts are not plastids. Lewitski * draws atten- 

 tion to the presence of minute bodies occurring in the proto- 

 plasm, but not in the nucleus, which he calls mitochondria, 

 chondriosomes, etc. These structures, which he considers are 

 essential parts of the cytoplasm, increase by division, and give 

 origin to the plastids. For instance in the pea, Pisum sativum, 

 and the asparagus. Asparagus officinale, the mitochondria of 

 the cells of the stem apex give rise to chloroplasts, whilst 

 those of the apex of the root are converted into leucoplasts. 

 Meyer,t however, is opposed to these conclusions. Miller J 

 finds that very minute chloroplasts occur in the cotyledons of 

 the seed of Helianthus annuus ; they increase in size and divide 

 by fission as germination proceeds and maturity is reached. 



Mottier § agrees that some forms of chondriosomes give 

 origin to chloroplasts and leucoplasts. He considers them to 

 be permanent structures of the cell, and that certain kinds 

 function as transmitters of hereditary characters. 



In green plants chlorophyll may occur in places where 

 light seemingly cannot penetrate, at any rate in any quantity, 

 for instance, in the cortex internal to the periderm — not only 

 in small twigs, but also of larger branches — in the medullary 

 rays and even in the pith.|| Chlorophyll also may be developed 

 in roots on exposure to hght, its formation being favoured by 

 conditions advantageous to carbon assimilation in the shoot. 

 It is developed in the cortex alone, e.g. Triticum, in the paren- 

 chyma of the vascular cylinder but not in the cortex as in 

 Rumex and Acer, and in both cortex and vascular cylinder 

 as in Zea.*^ Also it may occur in the cotyledons of seeds 



* Lewitski : " Ber. deut. bot. Gesells.," 1910, 28, 538. 



f Meyer : id., 1911, 29, 158. See also Schmidt : " Prog. Rei. Bot.," 

 1912, 4, 163; Forenbacher : "Ber. deut. bot. Gesells.," 1911, 29, 648; 

 Woycicki : " Sitz. Warschauer Ges. Wiss.," 1912, 5, 167 ; and Lowschin : 

 " Ber. deut. bot. Gesells.," 1913. 3«> 203. 



X Miller : " Ann. Bot.," 1910, 24, 693. A risume of the literature is 

 given by Cavers in " New Phyt.," 1914, I3» 96, 170. See also Guilliermond : 

 " Compt. rend. soc. biol.," 1921. 84, 197 ; 85, 462, 466 ; " Arch, biol.," 

 1921, 31, I. 



§ Mottier : " Ann. Bot.," 1918, 32, 91. 



II See Scott : id., 1907, 21, 437. \ Powell : id., 1925, 39, 503. 



