SEARS CROWELL 301 



The precise patterns of growth in hydroids tempt one to con- 

 struct mathematical models such as those which Fulton has devel- 

 oped and presented so well in this symposium. I am confident that 

 similar models could be constructed for Campamdaria. The pre- 

 ciseness of patterns also invites us to attempt to alter them. 



ALTERATIONS OF THE PATTERN OF GROWTH 



The basis for our first studies on Campanularia was the belief 

 that procedures which would alter the pattern of growth would 

 give some insight into the underlying controlling conditions. 

 Young colonies grown at different temperatures gave colonies or 

 similar form, but their growth schedule was strikingly altered. At 

 higher temperatures the apical growth of each new pedicel and 

 hydranth was accelerated, l)ut at cooler temperatures the initiation 

 of the growth of each new pedicel occurred so much sooner that 

 these colonies as a whole grew just as rapidly (7). 



This experiment showed that the factors which control the initi- 

 ation of new growth are different from those which control rate of 

 growth in an already established growing region. 



In a more elaborate experiment all growth zones and prospec- 

 tive growth zones were compared in colonies kept at different nu- 

 tritional levels. Figure 5 C shows diagramatically all of these zones. 

 It could be predicted that with sub-optimal feeding there must be 

 either a general uniform slowing down of all activities or a favoring 

 of some at the expense of others. The latter proved to be the case. 

 In general, lowered nutrition did not greatly affect the rate of 

 growth in an already established part, but it did delay or stop the 

 initiation of new growth. For example, the main stolon grew 

 almost as well in nearly starved specimens as in well fed ones, 

 and it produced new uprights. However, the initiation of subterminal 

 growth by the uprights was delayed. As a consequence of these two 

 effects the whole pattern of partly starved colonies was strikingly 

 different from that of well fed ones. The two were about equally 

 extensive along the substrate, but the height was conspicuously 

 different. 



