216 N. H. COWDRY. 



tion of mitochondria in different parts of plant cells one would 

 be inclined to examine cells polarized with reference to light, 

 secretion and so on, where cytoplasmic division of labor may be 

 expected. 



Morphology, 



As we pass down the plant scale we find no noteworthy differ- 

 ences in the morphology of mitochondria, even in those A Igce 

 which possess them they are alike. Similarly, few animals have 

 mitochondria of distinctive morphology, though in certain species 

 of both plants and animals, either filamentous or granular forms 

 may predominate. 



In the different tissues of plants there is some variation in 

 the size and shape of mitochondria. In some cells thick fila- 

 ments are most abundant, while in other kinds of cells, granular 

 forms of variable size may be found. Networks are rarely met 

 with. The question is complicated by the fact that in certain 

 tissues all morphological transitions between typical mitochondria 

 and true plastids are to be seen ; swellings develop in the region 

 of the mitochondrial filaments, which apparently grow larger 

 and larger and ultimately form mature plastids. 



In the different tissues of animals there is rather more varia- 

 tion in the morphology of mitochondria. They are usually 

 filamentous in gland cells, rod-like in muscle cells and they are 

 often granular in egg cells. Networks occasionally occur in the 

 pancreas and in spermatogonia as well as in other locations. 

 Even within gland cells of the zymogenic type there is consider- 

 able variation. The mitochondria in the acinus cells of the 

 pancreas are uniformly longer and thicker than those in the 

 chief cells of the fundus of the stomach and I find that they are 

 two or three times as long as those in the serous cells of the 

 parotid of the mouse (compare Figs. 2 and 16). The mito- 

 chondria in zymogenic cells often possess little enlargements 

 which are supposed to be the precursors of granules of zymogen, 

 and which call to mind the swellings on the mitochondria in 

 plant cells during plastid formation. The similarity of the 

 process may be seen by taking two specific instances; the pro- 

 duction of metachromatic corpuscles in plants as figured by 



