276 Non-Isolable Races. 
exceptions is Wcicjclia amabilis varicgata which was 
raised by VAN HouTTE 1 from the seed of the green 
variety; another is the variegated grape raised by 
KNIGHT. 2 In many cases a record of the original dis- 
covery has been preserved. Thus WOLFF 3 states that 
he found a variegated branch on a bush of Spiraea opuli- 
folia ; the leaves were whitish green with a sulphur yel- 
low margin, marked here and there with dark green 
flecks. The new form was easily multiplied by cuttings 
and appeared on the market as Spiraea opiili folia hetero- 
phylla fol. aur. marg. 
In nature bud-variations of this kind are also occa- 
sionally found, and it seems that this is almost the only 
bud-variation which is met with amongst wild plants, 
for usually this phenomenon is observed as a case of re- 
version on cultivated varieties or on hybrids. I myself 
have found very beautiful and large variegated twigs in 
Qiiercus pedunculata, Betula alba and Fagns sylvatica 
in the forests near Hilversum; in each case there was 
one large variegated branch on an otherwise green tree 
amongst hundreds or even thousands of perfectly green 
individuals. 
On the variegated branches the variegation often ap- 
pears unilaterally. The anomaly is developed laterally 
or unilaterally, or to use a more accurate expression, 
sectorially. For in the vertical projection of the branch 
there is usually only one sector which is variegated ; some- 
times one-half, sometimes one-third, and often even a 
smaller section of the circumference of the stem being 
affected. 4 The sectorial variation behaves in the same 
^ERLOT, IOC. Clt., p. 74. 
2 DE CANDOLLE, Physiologic, II, p. 734. 
s Gartenflora, Vol. XXXIX, 1890, p. 9. 
4 A study of sectorial variation in relation to the divisions in the 
