Cockayne. — Ecological Studies in Evolution. 7 



accumulates in any given direction individual differences in his domesticated 

 productions." And further on (p. 38), " Hence I look on individual 

 differences ... as of the highest importance for us, as being the 

 first steps towards such slight varieties as are barely thought worth record- 

 ing in works on natural history." De Vries and his followers, on the other 

 hand, deny that a fluctuating character can be accumulated indefinitely, 

 and affirm that, " Selection according to a constant standard reaches its 

 results in a few generations. The experience of Van Mons and other 

 breeders of apples shows how soon the limit of size and lusciousness may 

 be attained. . . . Improvements of flowers in size and colour are 

 usually easy and rapid in the beginning, but an impassable limit is soon 

 reached" (De Vries, 1904, pp. 806, 807). Further (p. 18), "Fluctuations 

 always oscillate round an average, and if removed from this for some time 

 they show a tendency to return to it. This tendency, called ' retrogression,' 

 has never been observed to fail as it should in order to free the new strain 

 from the links with the average." Again, " Fluctuations are not observed 

 to produce anything quite new, and evolution, of course, is not restricted 

 to the. increase of the already existing peculiarities, but depends upon 

 the continuous addition of new characters to the stock." The opinion of 

 Klebs cannot be overlooked in this matter. This famous investigator 

 has shown in his remarkable experiments (Klebs, 1903) that variations 

 can be artificially induced which are far beyond the limits of fluctuat- 

 ing variability and considerably greater than any mutations hitherto 

 recorded. 



Ecological observations can say little on a debatable topic like this, 

 where long-conducted experiments are alone of weight. Some observations 

 regarding vegetables which have escaped from cultivation in New Zealand 

 are not without interest, as showing reversion to the wild state. The radish 

 {Rhaphanus sativus L.) is abundantly naturalized near Wellington, but 

 the roots are no longer swollen to any extent. The parsnip (Peucedanum 

 ■sativum Benth. & Hook.), probably the celebrated " Student," which is 

 supposed by writers on evolution to be a fixed race,* came up year by year 

 in a neglected part of my garden, but in a much deteriorated form.f So, 

 too, with " improved " pansies, primroses, and polyanthuses^ in my garden, 

 and with Eschscholtzia califormoa as naturalized near Cromwell, Central 

 Otago. 



In many cases fluctuating variations are very small, and appear to 

 be neither an advantage nor the contrary to their possessor. In other 

 cases there are variations of much greater magnitude, which ecological 

 observations, as shown further on, prove to be distinctly dependent 

 upon external stimuli bringing about a response within the plant which 

 is manifested by a visible, morphological or an invisible physiological 

 change. 



"& x 



* Romanes (1895, p. 125) writes, " That is to say, it has oome true to seed for the 

 last forty years." Romanes mentions this case as an example in support of the heredity 

 of an acquired character, but Darwin (1905, p. 229) mentions it as a case of " methodical 

 selection." 



f With a species such as this it really must be nearly impossible to judge under 

 European conditions how far a supposed " wild " plant may be really wild and not the 

 descendant of a cultivated form. 



J The leaf-like calyx of the primroses, &c, known as " Jack-in-the-green " is a 

 remarkably persistent character. 



