132 The Romance of Wild Flowers 
Another tribe of the Geranium family is repre- 
sented in this country by the httle Wood Sorrel 
(Oxalis acetosella), one of the 
most beautiful of our wild 
plants. We may find it in all 
its chaste beauty in April or 
May, creeping over the leaf- 
mould and the decaying tree- 
trunk in moist woods, especially 
on a sandy soil. The creeping 
rootstock is slender and knotted, 
of a pinkish hue, and the leaves 
start directly from it on long 
foot-stalks. They are of the 
conventional shamrock pattern, 
divided into three broad heart- 
shaped leaflets, each having a 
distinct fold along the middle, 
and coloured with purple on the under-side. These 
leaves possess a considerable amount of sensitive- 
ness, even irritability. At night-time, or on the 
near approach of rain, each leaflet droops until the 
central “nerve” touches the leaf-stalk and the two 
halves of the leaflet are at right angles to each 
other. The object of this arrangement is doubtless 
that rain and moist air may get uninterrupted 
access to the rootstock and roots beneath. But if 
“the plant be grown in a pot and shut up for an 
hour or so in a dark cupboard, the leaves will be 
found to have assumed the nocturnal position—that 
is, the leaflets will be all folded down to their foot- 
stalks. If now the plant is brought out and exposed 
to full sunlight, the leaves will at once assume the 
Wood Sorrel 
