CHANDLER FULTON 295 



and advancing tip. This growth inhibition along an estabhshed 

 stolon may be related to the fact that Cordtjlophora, unlike hydra, 

 will not grow on the bottom of a Petri dish but needs to be suspend- 

 ed on a microscope slide in a beaker of water. The reason for this 

 "Fulton effect" as I call it, seems to be the greater sensitivity of 

 Cordylophora to pC02, for we have found that a pC02 as low as 

 1.5% atm. inhibits its growth while Hydra can stand up to 10% atm. 

 Thus, Cordylophora on the bottom of a Petri dish sits in its own 

 "halo zone" of high pCOo and inhibits itself, whereas Cordylo- 

 phora on a slide is continually bathed by the thermal currents that 

 exist within a beaker and can easily be shown with methylene blue. 

 Perhaps this apical inhibition of stolon growth by pCOi. may 

 partially explain the growth pattern of Cordylophora. 



