a 
368 Field, Forest, and Wayside Flowers 
almost completely the union between leaf and 
branch. Then, some frosty night, a thin plate of 
ice forms in the absciss layer, and the separation 
between leaf and branch is finished and_ final. 
When the morning sun melts the ice the leaves 
will shower from the boughs, however calm the air. 
And now Nature doctors the wound made by 
the leaf’s fall. The broken ends of the bundles of 
fibres and vessels left at the scar are covered (in 
many trees) with a protecting gum, and a little 
later they are encompassed by the growth of the 
cork-seal, and the healing of the scar is complete. 
The falling foliage of the horse-chestnut leaves 
scars large enough to show clearly the marks of 
Nature’s surgery. The cork-seal, which is much 
in evidence, has a horseshoe-shaped outline, and the 
slightly projecting ends of the fibro-vascular bundles, 
overlaid by a dark, glistening gum, suggest the 
horseshoe-nails (Fig. 99@). 
What falls from the bough in autumn is little 
more than the dead skeleton of the summer leaf— 
mere dry skin, empty cells, and stringy fibre. Al- 
most all the living substances which once filled the 
leaves were withdrawn from them before they fell, 
and are now safely stored away in trunk and boughs. 
Professor Von Sachs, author of the ‘‘ Physiology 
