STUDIES ON MITOCHONDRIA IN PLANT CELLS. 193 



An exposure to the same temperature for eighteen days ap- 

 parently brings about a breaking up of the mitochondrial fila- 

 ments into short rods and granules which stain intensely (Fig. 

 9). The protoplasm is also seen to be distinctly reticulate, the 

 mitochondria occurring in the denser strands. The more intense 

 staining of the nucleolus, shown in the figure, appears to be an 

 individual variation not associated with exposure to cold. 



Other plantlets which were placed in a freezing mixture of ice 

 and salt in the ice box for 20 hours show more advanced altera- 

 tions (Fig. 10), the mitochondria remaining about the same and 

 the protoplasm showing many scattered vacuoles, the reticulate 

 appearance having disappeared. 



The presence of distinctly filamentous mitochondria after a 

 sojourn of 4 days in the ice box tends to support Dubreuil's view 

 ('13, p. 137) that filamentous mitochondria are indicative of rest 

 and granular ones of active multiplication by division, because 

 it is safe to assume that the chemical changes in which the mito- 

 chondria are concemed share in the general retardation occa- 

 sioned by reduced temperature. Other important considerations 

 however show that this generalization does not hold (E. V. 

 Cowdry, '18, p. 67). 



7. Submergence in Water. 



Entire plantlets were submerged in ordinary tap water for 24 

 hours and thus deprived of the regular amount of oxygen. The 

 chief alterations are manifest in the inner cells of the cortex 

 (Fig. n), in which the mitochondria have broken up into rather 

 large short rods and granules which vary in their staining re- 

 action. The more superficial cells of the cortex, on the other 

 hand, show no characteristic changes, the mitochondria retaining 

 their normal filamentous shape. The controls showed a vary- 

 ing degree of vitality, about 50 per cent, being killed. 



8. Restricted Air Space. 



Plantlets were placed in a bottle, containing an air space of 

 about 15 c.c. and tightly closed with a paraffin-coated cork. 

 Preparations were made after 24 hours which showed a reversal 

 of the changes due to submergence ; for in this case the altera- 



