Introduction to Factors 307 



at first appear, may still be very fruitful. It is often possible to examine 

 the effects of changes in one factor without serious complications from 

 others, and the organism does remain essentially constant over short 

 periods. The very considerable knowledge now available as to the 

 factors that modify plant development has proved most important for 

 an understanding of the problems of morphogenesis, and there are wide 

 possibilities for extending it much further. The next seven chapters are 

 devoted to a brief consideration of the operation of these factors. 



