428 C. M. CHILD. 



The earlier data on Callithamnion (Child, 'i6a) are supple- 

 mented by observations on two more species, Callithamnion 

 Baileyi and a species resembling C. Baileyi in sympodial growth- 

 form but with a somewhat different order of branching and 

 strictly monosiphonous throughout, which it was impossible to 

 identify with certainty. 



In both these species the primary gradient in each unbranched 

 axis and each cell is basipetal as tested by killing with neutral 

 red alone, with KCN of various concentrations after neutral red 

 and by HgCl 2 w/5O,ooo. The basipetal gradient in single cells 

 even along the main axes is very distinct and shows few irregu- 

 larities in plants which are in good vegetative condition, provided 

 they are not killed too rapidly. 



As an axis gives rise to branches, however, the primary gradient 

 undergoes certain modifications which are very evidently asso- 

 ciated with the growth-form. These modifications concern the 

 susceptibility relations of different branches along an axis. In 

 general the farther from the apical end a branch arises the higher 

 its susceptibility, and the rate of growth of the branches shows 

 the same relation to the axis as the susceptibility, i. e., the more 

 basal branches grow more rapidly than the more apical. Both 

 of these features are associated with the sympodial growth-form 

 of these species and they are the reverse of the relations observed 

 in the monopodial C. roseum (Child, *i6a). A more extended 

 account of these modifications of the susceptibility gradient is 

 postponed to another time. 



Griffithsia. 



Griffithsia bornetiana, to which my attention was first called by 

 Professor Osterhout, has proved to be one of the most interesting 

 forms thus far examined, first because of the large size of the 

 cells and the conspicuous character of the death changes, and 

 second because the gradient very readily undergoes alterations, 

 both in nature and under experimental conditions. 



To the naked eye the color of the plant is usually rather more 

 reddish or less brown than that of most related forms. The 

 cells of the monosiphonous axis are readily visible to the naked 

 eye, the longer more basal cells being often several millimeters in 



