422 C. M. CHILD. 



from the part concerned. Where a main axis or a branch has 

 been bent sufficiently to crush or injure the protoplasm the 

 susceptibility is very high unless the protoplasm is already killed, 

 and death usually proceeds in both directions from such a point 

 of injury, but its progress basipetally is usually the more rapid. 

 In general the older parts of the thallus are likely to have received 

 a greater number of such injuries than the younger and the more 

 frequent irregularities in the gradients may be due in part to this, 

 but there is no doubt that with the slowing down of the activity 

 of the apical region of an axis, the gradient undergoes a leveling 

 down and slight local differences in activity in different regions 

 of the cell may determine irregularities in the course of death. 



In a plant so delicate as Bryopsis it would probably be very 

 difficult to obtain an axis with its branches which would show a 

 perfect basipetal death gradient in all parts. Not only the 

 greatest care in collecting and handling but also absence of 

 injury and a fairly uniform environment for at least a consider- 

 able period before collection would be necessary conditions. 

 The point of interest is not the appearance of local or regional 

 irregularities, which are to be expected, but the general regularity. 



There can be no doubt that the uninjured axis of Bryopsis, in 

 good physiological condition, whether it is a lateral branch or a 

 main axis, shows a basipetal susceptibility gradient, i. e., a 

 gradient in which the progress of death is basipetal and that 

 each system of axis and primary branches as a whole shows a 

 similar gradient. 



In my material, which had remained in the laboratory for 

 twenty-four hours before I obtained it, death was already begin- 

 ning in some of the axes, undoubtedly in consequence of labora- 

 tory conditions, as no special care had been taken to keep the 

 plant in good condition In all such cases the dead parts were 

 readily distinguishable from the living by their failure to stain 

 with neutral red, and it was observed that such death began 

 apically and progressed basipetally in each axis and system of 

 axes, i. e., the susceptibility gradient was the same as in KCN. 

 Scarcity of material made it impossible to test susceptibility 

 to other agents and conditions but the observations and experi- 

 ments on other species leave no doubt that the axial gradients in 



