620 Validity of the Doctrine of Mutation. 



instances of bud- variations the possibility of the plant 

 in question being- a hybrid has not been considered. A 

 single case has fallen within my own experience ; this is 

 a hybrid between Veronica longifolia and its variety V. 

 I. alba. The flowers of this hybrid are blue, and it may 

 easily be kept in cultivation for many years by means of 

 vegetative propagation. Ever since 1889, when I ob- 

 tained the first specimen, I have had many thousands of 

 stems in flower, arx)ngst which I observed several cases 

 of sectorial and of bud-variation, the last of them in the 

 summer of 1902. The bud-variation sometimes occurred 

 in the rhizome (1902) ; the whole shoot above the earth 

 lacked the red pigment, both in its bark and its flowers, 

 and so was easily recognizable before it bloomed. All the 

 flowers were white, whilst those of the remaining shoots 

 from the same rhizome were blue. Occasionally I found 

 a raceme witli white flowers arising as a lateral 1)ranch 

 from a stem on which the rest of the flowers were blue 

 (1894). The sectorial segregation is manifested in this 

 hybrid in such a way that one side of the raceme had blue 

 flowers, whilst those on the other were white. ^ The 

 breadth of the longitudinal strip bearing white flowers 

 is subject to variation ; it may be either a half of the whole 

 raceme (as in 1891), or a quarter (1898), or even less 

 (1894, 1895). The seeds of flowers which have thus 

 become white by vegetative mutation produce white- 

 flowered offspring, so far as I am able to judge from 

 some preliminary experiments. 



As is well known, Naudtn has crossed Datura Stra- 

 in oniiwi with D. Jaevis, and found amongst many hybrids 

 with exclusively thorny fruits, three individuals which 

 gave instances of vegetative segregation. These belonged 



* Bcr. d. d. hot. Gcs., igoo, XVIIT, p. 86. 



