AXIAL SUSCEPTIBILITY GRADIENTS IN ALGJE. 421 



a highly orderly pinnate arrangement of lateral branches is a 

 single cell. Unfortunately, owing to scarcity of material, it was 

 possible to examine only a few of the vertical axes with their 

 branches and these had been in standing water in the laboratory 

 for twenty-four hours before they were available. They were 

 first stained in neutral red and then placed in KCN m/$o in 

 Syracuse dishes covered with a thin glass plate and the course 

 of death observed under the microscope. 



In those axes which were still in good condition death began 

 in general at the apical end of each main axis and branch and 

 progressed basipetally and in each system of main axis and 

 branches as a whole a similar gradient appeared, the branches 

 nearest the apical end being most susceptible and death pro- 

 gressing basipetally from branch to branch. Moreover, at least 

 the younger branches were more susceptible than the level of 

 the axes from which they arose. 



It would, I think, be difficult to find a more beautiful example 

 of intracellular axial gradients in susceptibility than in Bryopsis. 

 As in other forms (Child, 'i6a) the first indication of approaching 

 death is a deepening of the neutral red tint in the cell as if the 

 protoplasm were becoming more acid. This change in color 

 occurs first apically and progresses basipetally and is followed 

 in a few moments by the disintegrative changes in the protoplast. 

 The progress of the coagulation and aggregation of the proto- 

 plasm into masses which are at first almost black in consequence 

 of the high concentration of the neutral red in them, but which 

 lose the stain soon after coagulation, can be followed under the 

 microscope from one level to another as a visible wave of change. 



As stated above, the course of death is in general basipetal, 

 but in the few axes examined there was none which did not 

 show some irregularities. In young growing axes the irregu- 

 larities are much less frequent than in old, where most or all of 

 the branches have completed their growth, and a larger or smaller 

 number of the more basal branches may be in part or entirely 

 dead when the plant is collected. Similarly, the more apical 

 younger portions of an axis with its primary branches usually 

 show fewer irregularities than the older more basal regions. 

 Injuries of course alter the gradient for a greater or less distance 



