136 INDIVIDUALITY IN ORGANISMS 



is accelerated. The same result may be attained by 

 compressing, sharply bending, or partially crushing the 

 stem at some point between the two ends. In such cases 

 the influence of the dominant apical region is prevented 

 from reaching the basal end, which is- therefore physio- 

 logically isolated and the establishment of the new 

 gradient but little retarded. Often also the develop- 

 ment of the basal hydranth can be accelerated by cutting 

 partly through the stem, so that only a slender organic 

 connection between the two ends remains. In these and 

 various other ways the controlHng influence of the apical 

 region can be demonstrated. 



Neither the inhibition of development of the basal 

 hydranth by paraffining the basal end or sticking it in 

 sand nor the partial crushing or bending of the stem at a 

 certain level influences the development at the apical 

 end except in very short pieces. In these, inhibition of 

 either end may accelerate the development of the other, 

 and a single instead of a double structure may result. 

 These experiments show that in the longer pieces 

 dominance extends chiefly in the direction of the original 

 gradient, and we find correspondingly that the new 

 gradient which arises at the basal end does not extend 

 very far from that end. If, however, inhibition of the 

 apical end be continued for a longer time, the gradient 

 at the basal end extends farther from that end. 



The length of the hydranths formed in very short 

 pieces is often, though not always, less than in longer 

 pieces, particularly in pieces from the more basal regions 

 of the stem. Driesch has made much of this point as 

 an indication that an adaptation of the length of the 

 hydranth to the length of the piece takes place in order 



