276 A^oji-Isolablc Races. 



exceptions is lJ\vgcIia aiuabilis varicgata which was 

 raised by Van Houtte^ from the seed of the green 

 variety; another is the variegated grape raised by 

 Knight.- In many cases a record of the original dis- 

 covery has been preserved. Thus Wolff^ 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 opulifolia hetero- 

 phylla foL aitr. 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 

 Qiiercns pednncnlata, Betula alba and Fagus syhatica 

 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.^ The sectorial variation behaves in the same 



^Verlot, loc. cit., p. 74. 



*De Candolle, Physiologic, II, p. 73\. 



^Garteniiora, Vol. XXXIX, 1890, p. 9- 



*A study of sectorial variation in relation to the divisions in the 



