AXIAL SUSCEPTIBILITY GRADIENTS IN ALGJE. 429 



length. Microscopically by transmitted light the color may be 

 described as a brownish pink. The cells are translucent and the 

 chromatophores and numerous nuclei are readily seen. Before 

 death the cell surface undergoes certain changes in appearance 

 resulting from the aggregation of minute granules or semi-fluid 

 particles, this change differing somewhat in degree in different 

 cells, even of the same plant, and with different agents. These 

 aggregations are not infrequently seen in living cells under other 

 natural or experimental depressing conditions and undoubtedly 

 result from the activity of the living protoplasm. The occurrence 

 of death, however, is indicated by the rapid diffusion of the pig- 

 ment out of the chromatophores and into the vacuole of the cell 

 which becomes a brilliant rose pink by transmitted light and with 

 the loss of the pigment the greenish color of the chlorophyl 

 becomes visible in the protoplasm. By reflected light cells 

 which have undergone this change appear orange yellow and 

 opaque. Diffusion of the pigment to the exterior may be very 

 slow, but there can be no doubt that this change marks the death 

 of the protoplasm, and it is so striking that its beginning and 

 course can be followed without the least difficulty. 



In examination of the gradient in Griffithsia the substances 

 KCN w/5O, OT/IOO; ethyl alcohol, 10 per cent., 5 per cent.; ethyl 

 ether, 3 per cent., 2 per cent., 1.5 per cent.; HgCl w/5OO,ooo, 

 w/25O,ooo, w/5o,ooo, m/i,ooo; CuSO 4 w/5O,ooo approx., have 

 been used and some observations on the axial differences in 

 susceptibility to high temperature and confinement have been 

 made. 



Within certain limits all these agents and conditions give the 

 same results in axes which are in good physiological condition 

 and in the active vegetative stage. The apical cell is most 

 susceptible, and the course of death is basipetal from cell to cell 

 and usually within the single cell in the more apical regions. 

 In the plants examined most of the older axes consisted of 12-20 

 cells and the gradient is very often perfectly regular in the first 

 5-8 cells from the apex downward. Below this modifications 

 and irregularities become more frequent, though the general 

 gradient is often very regular all the way to the base. In the 

 basal half of such axes the cells have commonly undergone a 



