AXIAL SUSCEPTIBILITY GRADIENTS IN ALG.E. 423 



susceptibility to KCN are simply a special case of a very general 

 relation between axiate organisms and their environment. 



Cladophora sp. 



Various specimens collected at various times, first stained with 

 neutral red, then killed in KCN m/$o, show a basipetal gradient 

 in staining and in death and decoloration. Apical regions stain 

 most rapidly and most deeply and staining progresses in general 

 basipetally. Death in KCN also begins apically and progresses 

 basipetally. Of course exceptions to this general rule appear 

 frequently, particularly in the older parts of the plant, w T here 

 the gradient has become less distinct, and environmental factors 

 may have affected one cell or another, or a group of cells. Never- 

 theless, the general basipetal course of death is apparent even 

 to the naked eye in plants previously stained with neutral red. 



As in Enteromorpha (Child, 'i6a) a branch is in general more 

 susceptible than that level of the axis from which it arises. 

 Death progresses to the base of the branch and the cell of the 

 axis from which the branch arises usually dies considerably later. 



As its ability to live under infavorable conditions would sug- 

 gest, Cladophora is very insusceptible to KCN. In KCN m/$o 

 death of the apical cells begins only after several hours and the 

 basal regions of the main axes die only after 20-30 hours. In 

 this respect it contrasts sharply with Bryopsis where death in 

 KCN w/5O begins in }/ I hour and the whole plant is dead in 

 2-4 hours. 



When Cladophora is killed in a sea-water solution of neutral 

 red alone, death and decoloration are much less rapid than in 

 KCN, requiring several days for completion, but the point of 

 chief interest is that the death gradient is the reverse of that in 

 KCN 777/50. Death begins in the basal region, progresses acro- 

 petally in each axis and the apical cells are the last to die. This 

 reversed gradient is like the acclimation gradient (Child, '13^, 

 '136, 'iy, Chap. III.) observed in animals, where the rapidity 

 and degree of acclimation vary directly with the rate of meta- 

 bolism or physiological condition in different regions when the 

 concentration or intensity of the external agent is not too high. 

 In true acclimation, however, there is more or less approach to 



