33. 

 rogena ration. This, hi* ova r, is not the ease lor in acids and basee the tad- 

 pole* In the higher and moro detrimental concent rations oaaao regenerating at 

 a time as early or earlier than the controls. In low oxygen regeneration 



ceases at practically tha aana tin? in all concentration*, while in low teaqpora- 

 tures, although tne period of growth la longer at tha lower tonne r-<-turas tha* 

 at tha hi^hor tomparss.turoe, the difference is not fUtfiftiftttt ti eotspenante the 

 difference la rate of regeneration, ao Ihs x&tlmate amount rogeneratei ie still 

 less at the lower than at the higher teiapmr^lur^s. 



The only tonsbla explanation »ee?r»e to be Uut the phenow?r.a of 

 growth and of differentiation in tha regenerating pirta nr& differently af footed 

 by t'.e environmental agents studied, thr t ie, tfcftt tat optima for these 

 phenomena are different «o that a hydrogen ion concentration, an oxygen content 

 or « temperature of tha surrounding medium which retards ono process way hate 

 no effect wpon the other. Thus ft hydrogen ion concentration or deficiency 

 in oxygen which causae a narked retardation to regeneration ssay h^sve no effect 

 upon differentiation, while a temy * r it -*ra vmich retards regeneration &rsrttly 

 nay have only a slightly retarding effect upon differentiation. 



That the three environmental factors etui lei may liffer this *ay 

 in regard to their relative effects upon regeneration ft«d differentiation seems 

 the mora probable since experiments show th«.t they do differ in their relative 

 effeots upon regeneration and survival or length of life, Thas a. concentration 

 of acids or bases or a deficiency of oxygen sufficient to completely chaoi 



regeneration is rapidly fatal, whila a tadpole may live forty-eight lays at a 

 temperature whioh completely prevents regeneration. 



