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, ariongst 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 with white flowers arising as a lateral branch 
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. 1 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, NAUDIN has crossed Datura Stra- 
monium with D. laeiis, and found amongst many hybrids 
with exclusively thorny fruits, three individuals which 
gave instances of vegetative segregation. These belonged 
1 Ber. d. d. bot. Ges., 1900, XVIII, p. 86. 
