134 VARIATION AND DIFFERENTIATION IN CERATOPHYLLUM. 



(11) On any axial division of the plant as whorls are successively 

 produced by a growing bud they are formed with ever-increasing con- 

 stancy to their type. This we have called the ' 'second law of growth 

 in Ceratophyllum. " The growing-point appears to be influenced in its 

 morphogenetic activity by its previous experience. 



(12) These two laws operate in branch production as well as in leaf 

 production in Ceratophyllum. 



Summarized statements of the detailed results and discussions of 

 the conclusions drawn from them will be found on pp. 26, 54-57, 88-92, 

 95, 106-108, 115, and 124 and need not be repeated here. 



The results of this study emphasize the necessity for a knowledge 

 of the laws of diif erentiation within the individual of characters as a 

 preliminary to the use of these characters in the study of the problems 

 of evolution. 



