432 C. M. CHILD. 



Cystoclonium and Agardhiella each macroscopic axis consists of 

 a single monosiphonous axis with its branches and the vegetative 

 tip is a single cell, while in Chondrus and Lomentaria each macro- 

 scopic axis consists of a number of monosiphonous axes and their 

 branches, and the vegetative tip consists of a group of cells, the 

 apical cells of the main monosiphonous axes. Since these plants 

 show very definite macroscopic axiation, it is of interest to deter- 

 mine whether general axial gradients exist in these axes. Such 

 gradients correspond to the general gradient in the system of 

 main axis and branches of Callithamnion. The use of neutral 

 red is not necessary with these four genera, for the changes in 

 color of the phycoerythrin with different killing agents and its 

 diffusion out of the cells indicate very clearly the differences 

 in susceptibility in different regions. 



Cystoclonium purpurascens, in the few fronds examined, was 

 found to possess a very uniform basipetal susceptibility gradient, 

 both in the single axes and in the frond in general. Some 

 branches of the frond are very evidently inhibited in their growth 

 and remain short (Kurztriebe) and it is of interest to note that 

 such branches almost always show a lower susceptibility than 

 those which have undergone more rapid growth. 



In Agardhiella tenera the gradient is also very uniformly basi- 

 petal in each axis for several millimeters below the apical end. 

 In KCN w/5O which is of course alkaline, the color changes from 

 the normal reddish brown to orange yellow, and this gradually 

 changes to green as the pigment diffuses out. In HC1 m/5 it 

 first becomes deep purple, and this gradually fades to a dull 

 purplish white with the loss of the pigment. In HC1 a distinct 

 basipetal decrease in cell turgor precedes slightly the first change 

 in color, and in KCN accompanies it. 



In well developed fronds the purple color begins to appear 

 apically after 15-30 minutes in HC1 w/5, and after two hours the 

 whole frond has become purple and the apical regions are fading 

 to whitish. In KCN m/$o the apical regions begin to turn 

 yellow after about one hour, and after 6-7 hours the change has 

 passed over the whole frond and the extreme apical regions show 

 a slight greenish tint. The final change to purplish white in 

 HC1 and to green in KCN is complete only after one or two days. 



