Production of Constant Races 243 



found in some races which under certain definite conditions lose 

 their colour or their virulence. Among the phanerogams the in- 

 vestigations of Schiibler on cereals afford parallel cases, in which the 

 influence of a northern climate produces individuals which ripen their 

 seeds early ; these seeds produce plants which seed early in southern 

 countries. Analogous results were obtained by Cieslar in his experi- 

 ments ; seeds of conifers from the Alps when planted in the plains 

 produced plants of slow growth and small diameter. 



All these observations are of considerable interest theoretically ; 

 they show that the action of environment certainly induces such 

 internal changes, and that these are transmitted to the next gene- 

 ration. But as regards the main question, whether constant races 

 may be obtained by this means, the experiments cannot as yet supply 

 a definite answer. In phanerogams, the influence very soon dies out 

 in succeeding generations; in the case of bacteria, in which it is 

 only a question of the loss of a character it is relatively easy for 

 this to reappear. It is not impossible, that in all such cases there is 

 a material hanging-on of certain internal conditions, in consequence 

 of which the modification of the character persists for a time in 

 the descendants, although the original external conditions are no 

 longer present. 



Thus a slow dying-out of the effect of a stimulus was seen in my 

 experiments on Veronica chamaedrys 1 . During the cultivation of 

 an artificially modified inflorescence I obtained a race showing modi- 

 fications in different directions, among which twisting was especially 

 conspicuous. This plant, however, does not behave as the twisted 

 race of Dipsacus isolated by de Vries 2 , which produced each year a 

 definite percentage of twisted individuals. In the vegetative repro- 

 duction of this Veronica the torsion appeared in the first, also in 

 the second and third year, but with diminishing intensity. In spite 

 of good cultivation this character has apparently now disappeared; 

 it disappeared still more quickly in seedlings. In another 

 character of the same Veronica chamaedrys the influence of 

 the environment was stronger. The transformation of the in- 

 florescences to foliage-shoots formed the starting-point ; it occurred 

 only under narrowly defined conditions, namely on cultivation as a 

 cutting in moist air and on removal of all other leaf-buds. In the 

 majority (^) of the plants obtained from the transformed shoots, 

 the modification appeared in the following year without any inter- 

 ference. Of the three plants which were under observation several 

 years the first lost the character in a short time, while the two others 



1 Klebs, Kumtliche Metamorphosen, Stuttgart, 1906, p. 132. 



2 de Vries, Mutatio-nstheorie, Vol. 11. Leipzig, 1903, p. 573. 



162 



