180 THE STEUCTURE OF FLOWERS. 



some 'Eupliorhias and Ghrysosjolenium, for instance, tlien the 

 visits of insects would bring the required stimulus to advance 

 the colour to a pronounced yellow ; and so petals, it may be 

 conceived, came into existence. 



Pale and White Varieties. — The paler tints or even a 

 total absence of colour may seemingly occur as a variety of 

 any plant. It is often a concomitant of habitual self- 

 fertilisation in cases where the variety or species is a 

 degradation from some conspicuous and brightly coloured 

 insect- visited form. White-flowered individuals often appear 

 as " sports " amongst seedlings ; the immediate cause of 

 which it would be difficult to assign, beyond the general 

 one of the absence of those nutritive conditions which are 

 requisite for colours, as occurs in Gladioli* 



White, however, is useful as a starting-point for florists' 

 flowers where great variegation is required. Thus M. 

 Vilmorin "f says that " in ten examples of variegation 

 which were produced under my own observation, the course 

 was always the same. The original plant, with flowers whole- 

 coloured, gave in the first instance a variety of flowers 

 entirely white ; afterwards, variegations were produced from 

 this white variety on its returning towards the coloured type. 

 . . . This pure white variety usually gives in the first sowing 

 a greater or less proportion of plants with flowers like those 

 of the coloured type ; but by careful selection through 

 several generations the pure white type is in most cases 

 completely fixed. ... It is only among the white varieties not 

 completely fixed that the variegations make their appear- 

 ance ; at first they exhibit narrow pencillings, the coloured 

 portion being only one-tenth, and sometimes only one- 

 twentieth of the whole surface ; but then in the following 



* Garden, 1880, p. 327. 



t Flore des Ser. et des Jard. de VEur., (Qard. Chron., 1852, p. 500). 



