2l8 N. H. COWDRY. 



plants. Generally, however, filamentous, rod-like, dumb-bell 

 and granular forms are met with. Filaments, when present, 

 have an astonishingly uniform diameter in the same cell, though 

 they may possess the swellings already mentioned. Segmenta- 

 tion of filaments is of common occurrence in both and it is possible 

 that a coalescence of granules may take place. In some tissues 

 there is considerable variation from cell to cell, while in others 

 the morphology of the mitochondria is quite uniform throughout- 

 Thus the "anthocyane" producing mitochondria, figured by 

 Guilliermond ('130, p. 479), are uniform; those in the cortical 

 cells of the pea radicle, variable in length. In neighboring acinus 

 cells of the pancreas of the mouse they are uniform; in con- 

 tiguous spinal ganglion cells, variable. 



A fundamental distinction may be made between variations 

 in length and variations in breadth, in the case of both plant and 

 animal mitochondria, to which I have seen no reference in the 

 literature. While the mitochondria in the cells of the pea 

 radicle vary greatly in length, filamentous and rod-like forms 

 predominating, their girth is remarkably uniform, throughout 

 the whole tissue, in individual cells and in different parts of the 

 same filament (Fig. i). The same holds for the pancreas (Fig. 2). 

 The uniformity in girth extends right to the end of the filaments 

 which always end abruptly without tapering. The truth of this 

 statement is made still more apparent by examining any illustra- 

 tion of mitochondria, because artists are wont, quite rightly, to 

 draw each filament with a single sweep of the same pen or brush. 

 The one great exception to this rule is plastid formation in plants 

 and the production of bleb-like swellings in association with 

 secretion in animal cells. The diameter of the mitochondrial 

 filament is fixed, but the length is not; one is stamped on the 

 cell through its organization and is probably dependent on the 

 water content of the surrounding cytoplasm, the other is most 

 likely an expression of growth by accretion affecting the length 

 but not the diameter. We have here two attributes, independ- 

 ently variable, which may perhaps be influenced in different 

 ways, common to both plant and animal mitochondria, which 

 speak more strongly for their identity than any other. 



