INT.] ON NORMAL GROWTH 287 



These results indicate that during later development growth 

 is largely effected by excessive assimilation or by storing up 

 formed substance. 



From another standpoint we can recognize two kinds of 

 growth : one a transitory growth, after which the enlarged 

 organ may return again to its former size, and the other a per- 

 manent or developmental growth, which is a persisting enlarge- 

 ment, and plays an important part in development. As an 

 example of transitory growth may be cited the case of the Sen- 

 sitive Plant, whose leaflets when touched turn upwards as a 

 result of the growth of cells on the convex side ; but this 

 enlargement is only temporary -- it is transitory growth. 

 This phenomenon is indeed usually not included in the idea of 

 growth ; yet it is well-nigh impossible to draw a sharp line of 

 distinction between it and permanent growth. For example, 

 when a tendril of the Passion Flower is touched it may curve 

 as a result of growth of the cells on the convex side, and this 

 curvature may later become obliterated, as in the case of the 

 Sensitive Plant ; but the longer the contact is continued the 

 more the cells enlarge, and the more their walls become perma- 

 nently modified. Thus the condition of temporary growth 

 shades insensibly into that of permanent growth. So far as 

 possible we shall consider in this book only developmental 

 growth. 



Still another classification may be made of the phenomena of 

 growth. We may distinguish between diffused and localized 

 growth. In diffused growth the entire individual or many of 

 its parts are involved. In localized growth the process is con- 

 fined to a limited region. Thus in the early development of 

 the frog diffused growth occurs, while in the formation of the 

 appendages we have an example of localized growth. Since 

 localized growth is an important factor in differentiation, many 

 of the data concerning this phenomenon will be first considered 

 in the Part dealing with Differentiation. 



Normal growth may or may not be accompanied by cell-divi- 

 sion. But usually cell-division occurs sooner or later- in the 

 growing mass. The act of cell-division seems to retard the 

 process of growth. This conclusion follows from some experi- 

 ments of WARD ('95, p. 300) on the growth of bacteria, which 



