THE AXIXI. (.kADII-lNTS IN H VDRi /< ' \ . 



[87 



new polarities, the hydranth-stem axis being determined as a 

 .gradient by the greater respiratory activity occurring on the 

 upper free Mirtace. the stolon axis by -ome local region of greater 

 activity on the margin. 



22 



-'S 





I -ually, liouiAc-r, acclimation or recovery oc< m- -o -lo\\ 1\ that 

 the < nit^r >\\ ill- u'liich arise from these spherical ti uni-- are at in>i 

 Moli ui- ami only later transform into, or give rise t" hydranth- 

 >tcm axes. In many of these cases there can he no dotiht that 

 m \\ uiadii-nt- or axes originate since three and not infrequently 

 four -tolon> may arise from a single individual I igs. Jj 26, all 

 \ie\\i-d from a hove). These axes, or at le..~t ~me of them, are 

 e\idi-ntly "adventitious," i.e., they are determined hy -li^ht 

 I chance ilittm-nces among the cell>. each -tolon originating 

 as a locali/ed region in which the cellular activity i- yreatrr than 

 in Mirroundin^ n -ions. This region heiiins to -p.\\ at the 

 r\])en-e of other p.irts about it and as it grow- the gradation in 

 acti\ it\ . which i> at first about a center become- an axial gradient 



Drouth |iron-i-d>. Each outgrowing -tolnn i- -uch a gradient 



