FACTORS OF ORGANIC EVOLUTION. 459 



prove tliat those which are lost are any the less due to the impinging 

 stimuli. Those who write of definite variation usually construe the 

 result or outcome of some particular evolution into a measure of the 

 variation which is conceived to have takeu place in the group. Most 

 or all of the present characters of any group are definite because 

 they are the survivals in a process of elimination; but there may have 

 been, at various times, the most diverse and diffuse variations in the 

 very group which is now marked by definite attributes. As the lines 

 of ascent developed, and generation followed generation in countless 

 number, the organization was more and more impressed with the 

 features of ancestral characters, and these ancestral characters are the 

 more persistent as they have been more constant in the past. But 

 these characters, which appear as heredity or atavistic variations in 

 succeeding generations, were no doubt first, at least in the plant crea- 

 tion, theoft'spring, for the most part, of the environment reacting upon 

 the organism. As life has ascended in the time scale and has become 

 increasingly complex, so the operation of any incident force must ever 

 produce more diverse and unpredictable results. What I mean to say 

 is that, in plants, some of the variations seem to me to be the resultants 

 of a long line of previous incident impressions, or have no immediate 

 inciting cau^e. Such variation is, to all appearances, fortuitous. It is, 

 therefore, evident that the study of the effects of impinging environ- 

 ments at the present day may not directly elucidate the changes which 

 similar conditions may have produced in the beginning. 



While the steadily ascending line of the plant creation was fitting 

 itself into the changing moods of the external world, it was at the same 

 time developing an internal power. Plants were constantly growing 

 larger and stronger or more specialized. The accumulation of vital 

 energy is an acquired character the same as peculiarities of form or 

 structure are. It is the accumulated result of every circumstance 

 which has contributed to the well-being and virility of the organism. 

 The gardener knows that he can cause the plant to store up energy 

 in the seed, so that the resulting crop will be the larger. Growth is 

 itself but the expression or result of this energy which has been picked 

 up by the way through countless ages. Now, mere growth is variation. 

 It results in differences. Plants can not grow without being unlike. 

 The more luxuriant the growth, the more marked the variation. Most 

 plants have acquired or inherited more growth force than they are able 

 to use because they are held down to certain limitations by conditions 

 in which they are necessarily placed by the struggle for existence. I 

 am convinced that many of the members of jilants are simply out- 

 growths resulting from this growth pressure, or, as Bower significantly 

 speaks of them,' the result of an "eruptive process." The pushing out 

 of shoots from any part of the plant body, upon occasion, the normal 

 production of adventitious plantlets upon the stems and leaves of some 



' A Theory of the Strobilus in Archegoniate Plants, Annals of Botany, viii, 358, 359. 



