434 c - M - CHILD. 



apical regions have been observed and in low concentrations of 

 KCN w/5OO the color-change begins only after 3-5 hours and 

 appears first in the middle region of the main branches and stems, 

 i. e., the regions which are least susceptible to the higher con- 

 centrations. From these regions it progresses acropetally and 

 basipetally the tips of the branches being usually the last parts 

 affected. With concentrations of KCN 'between m/^oo and m/^o 

 or in plants which are somewhat more susceptible to 772/500, 

 mixed gradients may appear. The color-change may begin and 

 progress basipetally in the apical regions and later it may begin 

 in the middle region and progress more or less acropetally. In 

 plants kept in the laboratory for several days the gradient shows 

 a partial reversal, the susceptibility of the apical 3-5 millimeters 

 of many branches being lower than that of the levels next below. 



Chondrns crisptis, the common "Iceland moss" with flattened 

 dichotomously branching body, shows a very beautiful basipetal 

 gradient in KCN w/5O, alcohol 5 per cent., and HC1 m/io. The 

 first change in color from the deep red-brown or purple-brown 

 appears in the median apical region of each ultimate branch and 

 progresses laterally and basally in extremely regular manner. 

 In KCN this first change is to whitish green, in alcohol to a 

 rose-red or pink, in HC1 to a fine violet or purple. Following 

 this change in color there is gradual loss of the pigment by dif- 

 fusion to the exterior, and the plant becomes whitish and finally 

 almost pure white in KCN and alcohol and white with a trace of 

 purple in HC1. This loss of pigment also begins in the apical 

 region and progresses basipetally. In the concentrations men- 

 tioned above the first change in color begins in 1-4 hours and after 

 30-40 hours the loss of color is complete even to the base. 



In plants which are in bad condition, those which have been 

 torn loose and washed about by waves, the susceptibility is in 

 general lower and often lowest of all in the apical regions. 

 Where part of a frond has been torn or broken off and new axes 

 have recently regenerated on the old basal portion the young 

 axes show a much higher susceptibility than the old portion. 



Tests of susceptibility with KCN m/^o and HgCl 2 m/^o,ooo 

 both without and after neutral red, and with neutral red alone, 

 made on a few plants of Lomentaria uncinata found detached in 



