2o< i 



THE AMERICAN NATURALIST [Vol. XLII 



of a group, by which amplitude of variation and mode 

 of ontogenetic procedure may be accurately outlined. 



The development of this aspect of natural history has 

 been followed by a truer estimation of capacities and 

 activities as attributes of organisms, with the result that 

 even morphology has come to be based upon physiolog- 

 ical principles, upon which alone it may make further 

 material progress. 



The groups with which the physiologist deals in the 

 detection of activities, estimations of functions and 

 measurements of performance, consist of a series of 

 generations of individuals through which identical qual- 

 ities, characters and capacities are transmitted uniformly 

 within the limits of fluctuating variability. These 

 groups may sustain the most diverse relationship and 

 all possible degrees of affinity, but differ essentially in 

 their physiological response to any given environment 

 under permanent existence in it. 



To test such conceptions of hereditary entities implies 

 pedigreed cultures, or observations upon lineal series 

 under known conditions of descent, hybridization opera- 

 tions and statistical estimations. The various qualities 

 do not display themselves equally throughout the meta- 

 meres of the sporophyte, and it is by no means to be 

 assumed that the flower, or the terminal portion of the 

 shoot surviving at maturity, is a compendium of the 

 various developmental stages. Nowhere is this more 

 beautifully apparent than in intermediate hybrids of the 

 first generation, in which the <|inilities of one parent pre- 

 dominate in the leaves and the other organs of the first, 

 or lower internodes, while those displayed by the upper 

 terminal portions of the stem and flowers may be those 

 of the other parent. Kxemplifications of this fact have 

 also been observed, in which the internodes and the 

 organs formed during the first season's growth in two 

 nearly related forms were widely different, displaying di- 

 vergent structures and different 1 'nasties" and tropisms. 

 During the second year's growth, the organs formed 



