THE STRUCTURAL COMPONENTS OF PROTOPLASTS 



35 



ally to disappear as differentiation approaches completion. Special 

 techniques are required for their study in fixed preparations. They 

 can be well fixed with fluids containing formalin and potassium dichro- 

 mate, but both they and the proplastids are dissolved by some of the more 

 highly acid fluids, especially those containing acetic acid, commonly used 

 for the preservation of nuclei. 



There is a verj^ large bodj' of literature on the subject of chondrio- 

 somes, but they are still an enigma to the cytologist. Naturally many 

 suggestions have been made regarding their significance. For the most 

 part these fall under two general heads: (1) the view that they are reserve 

 products or by-products of some form of cytoplasmic activity common to 

 nearly all organisms, these prodvicts being utilized as energy sources or in 

 other ways ; (2) the view that they are organs or organ-like bodies playing 

 a definite role in the elaboration of metabolic products or in differentiation. 



A 





. ' c * d 



Fig. 22. — Choiidiiosoiae?. in liver cells of fishes, a ncHinal cell from Fundulus kept at 

 temperature of 21°C.; b, cell from Fundulus kept at temperature (37.5 to 40°C.) inducing 

 heat rigor; c, cell from Fundulus in extreme heat rigor induced at 45 to 50°C.; d, normal 

 cell from goldfish. {After R. C. MacCardlc.) 



The first of these views was suggested by the decrease in abundance 

 and frequent disappearance of the chondriosomes as tissues mature and 

 by their apparent use in the elaboration of secretion products in certain 

 gland cells. The second view was suggested by what was interpreted as 

 the direct transformation of chondriosomes into various intracellular 

 specializations, such as myofibrils and neurofibrils, the chondriosome 

 being looked upon as a sort of organ of differentiation. Organ-like roles 

 in connection with enzj'me activity, secretion, respiration, and adsorption 

 catalysis have also been regarded as possibilities. Of particular interest 

 was the observation that the chondriosomes bear a striking resemblance 

 to young plastids in form, chemical composition and specific gravity; 

 in fact, many cytologists have inclined to the view that plastids arise in 

 plant cells by the transformation of chondriosomes of a certain type. 



The problem of chondriosome-proplastid relationship has been a par- 

 ticularly vexing one for a number of years. Recent work on the shapes, 

 color reactions, and pigmentation of these bodies has emphasized anew 

 their apparent distinctness (Figs. 23, 24), whereas some observers are 



