124 INTRODUCTION TO CYTOLOGY 



physiological role of such changeable types of chondriosomes is that they 

 have to do with the processes of oxidation and reduction — with cellular 

 respiration. It is also becoming increasingly apparent that other chon- 

 driosomes represent the juvenile stages in the development of plastids 

 of various kinds, and that they are in some way concerned in the forma- 

 tion of chlorophyll and other pigments. If this is true they are clearly 

 of the highest importance. 



Whether or not any of the chondriosomes are to be considered as 

 permanent cell organs is a question to which, in view of the conflicting 

 testimony of competent observers, no final answer can at present be 

 given. To determine whether these minute bodies arise de novo or 

 always multiply by division is a matter of extreme practical difficulty. 

 Until this question is settled it is obviously impossible to come to a deci- 

 sion regarding the individuality of those plastids which appear to take 

 their origin from chondriosomes, or to know what may be the possible 

 relation of chondriosomes to inheritance. With respect to the latter 

 point, the chondriosomes, like all other structures concerned in meta- 

 bolism, may be indirectly associated with the development of hereditary 

 characters, but the view that they transmit or represent differential 

 factors for such characters is as yet unsupported by adequate evidence. 



From the fact that the chondriosomes may not preserve their indi- 

 viduality at all times, however, it does not follow that they must be denied 

 the rank of cell organs. Their great variability, indifferent behavior at 

 the time of cell-division in so many cases, and their unknown mode of 

 origin are, as Kingsbury (1912) states, against the view that they are cell 

 organs; and it is doubtless true that many chondriosomes should for such 

 reasons be denied such rank. On the other hand, those chondriosomes 

 which seem clearly to perform important and specific functions in the life 

 of the cell should, like centrosomes appearing de novo at each cell-division, 

 be looked upon as cell organs, though not as permanent ones with an 

 uninterrupted continuity. 



In spite of the fact that the study of chondriosomes has so far raised 

 more problems than it has solved, it has already proved of much value, 

 for it has turned to the cytoplasm some of the attention so long directed 

 almost exclusively to the nucleus, and it appears that many problems of 

 much importance to cytology pertain to the cytoplasm. It has also 

 been of great service in bringing about a closer scrutiny of the effects 

 of fixation and a renewed emphasis upon the importance of the study of 

 living protoplasm. Much has already been learned as the result of this 

 study, but the solution of the principal problems involving chondriosomes 

 must await the results of further research. 



