92 INTRODUCTION TO CYTOLOGY 



4.2 to 5.2 and are destroyed by more acid fluids, and the term "plastids" 

 only for those bodies containing starch or chlorophyll. We have here 

 chosen somewhat arbitrarily to retain the term " chondriosome " but to 

 restrict its application to those elements with a fairly characteristic 

 composition which do not behave as the primordia of plastids. When the 

 nature of a small element is unknown, such non-committal terms as 

 "microsome" and "particle" are always available. It remains for 

 future research to reveal more precisely the chemical and genetic relation- 

 ship of proplastids and chondriosomes at the time of their first appearance 

 in the cytoplasm and to evaluate the claim of Meyer and others that the 

 chondriosomes are, like all other formed bodies in the cytoplasm except 

 plastids, ergastic in nature. 



Conclusion. — In the present state of our knowledge no final judgment 

 can be rendered on the question of the nature and function of "chondrio- 

 somes." Bearing present probabilities in mind, we may adopt as a 

 tentative working basis the view that in both plants and animals the 

 chondriosomes, or mitochondria, are a special class of small bodies fairly 

 distinguishable chemically from other materials of an ergastic nature, 

 that they represent elaborated products which are somehow employed 

 as sources of matter and energy for further growth and differentiation, 

 and that they are best regarded as distinct from the plastids of plant cells. 

 This provisional disposition of the matter will be convenient until wholly 

 decisive evidence is obtained. 



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

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

 turned to the cytoplasm some of the attention so long directed almost 

 exclusively to the nucleus. 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. 



