PLASTIDS AND CHONDRIOSOMES 



121 



chick embryo. They believe that the chondriosome elongates and 

 directly becomes the young fiber. Gaudissart (1913), on the contrary, 

 shows that the fiber does not arise exclusively from the chondriosome, but 

 that the primary basis is furnished by the plasmatic reticulum with 

 which the chondriosomes cooperate in building up the fiber. Although 

 the chondriosomes thus have a part in the genesis of the muscle fiber, 

 the latter is not a "modified filamentous chondriosome," as Duesberg 

 believed. 



Hoven (1910a) and Meves have similarly attempted to show that 

 chondriosomes are concerned in the differentiation of neurofibrils and the 

 collagenous fibers of cartilage. Regaud (1911), Guilliermond (1914), 



:. '; :;: d 







^ O <S 



FIG. 46. 



A, formation of fat in cell of rabbit by granular and rod-shaped chondriosomes. (From 

 Guilliermond, after Dubreuil, 1913.) B, formation of needle-shaped crystals of carotin in 

 chromoplasts derived from chondriosomes in epidermal cell of Iris petal. (After Guillier- 

 mond, 1918.) (7, chondriosomes and chloroplasts in young cell of Pinus banksiana. X 750. 

 (After Mottier, 1918.) D, transformation of plastid primordia into leucoplasts in root 

 cell of Pisum; some of the leucoplasts contain starch. (After Mottier.) 



Hoven (19106, 1911), and Lewitski (1914) have thought that the chon- 

 driosomes may in some cases perform a secretory function, and Dubreuil 

 (1913) has associated them with the production of fat (Fig. 46, A). In 

 the oocyte of Cicada Shaffer (1920) finds them transforming into yolk 

 spherules. The activity of bodies called " plastochondria " by Wildman 

 (1913) in the elaboration of the food supply in the spermatozoon of 

 Ascaris has already been mentioned. 



Relation of Chondriosomes to Plastids. One of the most conspicuous 

 views regarding the significance of chondriosomes is that which holds 

 some of them to be the primordia of plastids. After studying the cells of 

 Pisum and Asparagus Lewitski (1910) concluded that the chondriosomes 

 are essential constituents of the cytoplasm, and that they develop into 

 chloroplasts and leucoplasts in the cells of the stem and root respectively. 



