PLANT ZEBRAS 153 
IIS SS TEISIES Sri Sree 10 03S al Aan emt 
passed on to the offspring, most seedlings having 
similar purple leaves, though some individuals are 
green. The peculiar colour is due in this case to a 
pigment in the epidermis of the leaf; the green chloro- 
phyll is duly present, though its colour is masked by 
the purple leaf-skin. To a different category belong 
the “gold” and “silver” variegations which are so 
much exploited in shrubberies and borders and green- 
houses. These spots or stripes or tintings of pale 
colour on the leaves are due to the lack of chlorophyll 
in the chromatophores (chlorophyll corpuscles) ; some- 
times to an absence of the chromatophores them- 
selves; and this omission appears to be caused by an 
enfeebled condition of the plant. Variegated plants 
are weaker than normal ones, and hence do not tend 
to survive in nature. But gardeners have protected 
and propagated a large number of them. When the 
variegation arises, as it often does, on a branch of an 
otherwise normal plant, it usually is not reproducible 
from seed, and must be perpetuated by cuttings. But 
where it happens with seedlings, it is often more or 
less fixed, and may be reproduced generation after 
generation, as in the Golden Elder, Golder Feather, 
and the marginal-variegated form of Winter Cress 
(Barbarea vulgaris). 
Flower colour is not so fixed as leaf colour, for 
obvious reasons, the green colour of leaves being due 
to chlorophyll, which is an absolutely necessary 
ingredient of the leaf if plant food is to be manu- 
factured; whereas flower colour is merely for adver- 
tisement, and any pigment can be made to serve. In 
nature most flowers vary in tint, and some in a marked 
degree—take the little native Milkwort (Polygala), 
