INFLUENCE OF ENVIRONMENT 307 



determined. Extensive experiments have 

 been made within recent years on developing 

 animals and plants in order to discover the 

 factors involved in development, and the modi- 

 fications which may thus be produced are very 

 striking. 



B. EXPERIMENTAL MODIFICATION OF 

 DEVELOPMENT 



The study of development under experi- 

 mental conditions has given rise to a new 

 branch of biology, viz., experimental embry- 

 ology or the physiology of development. By 

 changes in environmental conditions notable 

 modifications may be produced in adult or- 

 ganisms, but these modifications are much 

 greater when the changed environment acts 

 on the organism during the period of its de- 

 velopment. 



I. Developmental Stimuli 



It is by no means easy to define such gen- 

 eral terms as "environment," "stimulus," "re- 

 sponse." In its common use "environment" 



