626 Validity of the Doctrine of Mutation. 
a hybrid may have been made on a normal plant, as 
WILLE has told me he suspects to be the case in the sup- 
posed graft hybrid consisting of a pear worked on a 
white thorn stock. 1 
The reader who is interested in the direct influence 
of the stock on the grafted bud is referred to the recent 
exhaustive studies by L. DANIEL. 2 
By pruning Cytisus Ad ami, BEYERINCK obtained very 
important results on the vegetative segregation of hy- 
brids. He found that buds which, as a rule, are resting, 
but which can be made to develop by cutting off the 
higher branches, tend to produce the characters of C. 
Laburnum or of C. purpurcus, so that we have it in our 
power to multiply the number of such segregations at 
will. More than one hundred instances were obtained 
by him on some few trees. Sectorial segregations of 
buds also occurred, sometimes transforming a longitu- 
dinal half of a shoot into C. Laburnum, whilst the other 
half remained C. Adaiui." It is to be expected that the 
application of this principle to other cases will lead to the 
discovery of important facts. 
Of the numerous instances of bud-variations de- 
scribed in the literature of this subject, many are, with- 
p. 237. Also LAURENT, loc. cit., p. 16. For a general review *of graft 
hybrids see FRUWIRTH, Zi'ichtimg landwirthschaftlicher KulturpUan- 
zcn, p. 72 ff. 
1 N. WILLE, Mittheilungen d. biolog. Gesellschaft in Christiania, 
Biol. Centralblatt, 1896, Vol. XVI, No. 3, p. 126. Perhaps this may 
be Pyrus auricula ris (P. coinmunis X Sorbus Aria} or a related hy- 
brid. See DIPPEL, Handbuch dcr Laubholzkundc, III, p. 359. 
2 LuciEN DANIEL, La variation dans la grcffe ct Vhcrcditc dcs 
caracteres acquis, Ann. sc. nat. bot, 1899, VITIth ser., Vol. VTTT. 
pp. 1-226 and Plates I-X, and the subsequent publications of the 
same author. 
3 M. W. BEYERINCK, Kon. Akad. v. Wetensch., Amsterdam, Nov. 
1900. 
