UNFOLDING OF WOOD SORREL LEA VES. 143 
flat, the leaflets being set at right angles to the stalk. But how 
did the leaf grow like this? or did it grow out of the ground in 
exactly this form and shape ? This latter alternative would be 
well-nigh an impossibility, for then the leaf would offer a large 
plane of resistance to the overlying soil. As a matter of fact it 
offers the smallest point possible — only the top of the bent stalk, 
as shown in fig. No. 1, where the leaf is hardly to be recog- 
nised at all. In the next stage the leaf is beginning to open, 
and here the three leaflets may be distinguished. They are (as 
in fig. 2), all folded down their mid-ribs, and lying side by 
side, the middle one projecting slightly beyond the others. In 
fig. 3 the leaflets have moved apart, the side ones moving 
sideways and the middle one up and back, at the same time 
they open slightly, as shown in fig. 4. In figs. 5 and 6 
further positions may be traced ; the middle leaflet having 
gradually raised itself to an upright position is now turning 
over, and the side leaflets have moved downwards and back- 
wards, until, as in fig. 7, they all hang unfolded round the stalk. 
After this the leaflets move upwards, at the same time unfolding 
completely, until they form the flat, three-divisioned leaf which 
we set out from. 
6 a 7 8 9 
In this way the middle leaflet not only revolves through about 
three-fourths of a circle, but afterwards reverses its motion, 
until it is about at right angles to the stalk, and during all this 
complicated motion the movement of growth is being also 
carried on. 
