382 LIBBIE H. HYMAN. 



a dagger in Table V. The average difference between the 

 number of hours required for the emergence of the hydranths on 

 apical and basal halves was 10 hours in exp. 9; 20 hours in exp. 

 17; 12 hours in exp. 29; and 8 hours in exp. 45. The individual 

 differences range from half an hour to more than forty hours. 



It may be inquired why in a small percentage of cases the basal 

 piece precedes the apical piece in regeneration, and why there is 

 such a great variation in the difference between the time of 

 regeneration of the two pieces. It is highly probable that these 

 variations are related to the degree of physiological isolation 

 existent in the basal pieces before they were cut from the stems. 

 It has already been pointed out that a hydranth controls only a 

 certain length of the stem proximal to it and beyond that limit 

 a new individual arises which eventually expresses its presence 

 by the formation of a lateral bud. Now it is evident that such 

 new individuals must exist physiologically before they give 

 morphological expression of their existence by bud formation. 

 It has already been stated that in these experiments the longest 

 obtainable stems free from buds were used. Such stems are 

 the exception rather than the rule since the majority of the 

 material obtainable, particularly in the summer, will furnish 

 only a small proportion of long stems free from branches. It is 

 therefore obvious that the basal regions of such long stems must 

 be in various stages of the process of physiological isolation and 

 branch formation. The nearer such basal regions are to branch 

 formation the more rapidly will they regenerate when isolated 

 and those that are on the very verge of branch formation may 

 conceivably regenerate as rapidly as or even more rapidly than 

 more apical pieces. This matter is referred to again in connec- 

 tion with experiments on the rate of regeneration of basal pieces 

 cut below branches. 



7. Remarks on the Temperature Coefficient. It has generally 

 been accepted that when the rate of a biological process increases 

 two to three times with each ten degrees rise in temperature 

 that such a process is chemical in nature. It may be doubted 

 that this line of reasoning is strictly correct. The use of the 

 temperature coefficient to analyze the nature of a biological 

 process involves the unwarranted assumption that such processes 



