302 



THE BIOLOGY OF HYDRA : 1961 



It is easy to conjecture that this difference is adaptive in na- 

 ture: It is better for a colony at an unsatisfactory feeding site to 

 move along than to add more feeding units where it is. 



Fig. 5. Campanularia. A. Technique of subculturing by placing an up- 

 right beneath a thread which has been tied around a slide. The new growth 

 is suggested by the dotted line. B. Pattern of a colony of the age used in 

 the nutrition experiment discussed in the text. The numbers designating 

 age of the upright correspond with those in Fig. 6. C. The zones of growth 

 and prospective growth in Campanularia are indicated: W. to Z. (With 

 permission; Fig. 1 of ref. 4). 



AGING 



The most striking observation, by serendipity, in the experi- 

 ment just discussed was that the increase in height of the older 

 uprights (stems with their hydranths) was much more adversely 

 aflFected by reduced nutrition than the comparable growth of young- 

 er uprights in the same colony. The growth in length of the up- 

 rights depends on recurrent initiation of each new node— it is 



