392 Field, Forest, and Wayside Flowers 
lies just behind the root-tip, ready to put out fresh 
root-hairs as soon as spring returns. 
While the root-tips are being enclosed in cork- 
sheaths, preparations for a long winter sleep are 
going forward among the branches overhead. 
All the trees which wear union suits of cork have 
on their youngest branches little ventilating holes, 
called ‘‘lenticels.’’ These can be plainly seen on 
the twigs of birch, beech, cherry, and elder, as 
rough oval dots, slightly raised, and different in 
color from the bark around them (Fig. 102). 
Those of the birch become greatly extended as 
time goes on and appear as sharply-drawn, blackish 
stripes, running horizontally around the trunk. But 
on the roughened older bark of most species of 
tree the lenticels are hard to find, though they are 
still there. 
In the older bark of the cork-oak, however, we 
know them only too well, for the brown, powdery 
streaks which sometimes run through bottle-corks, 
and cause them to crumble vexatiously when one 
tries to draw them, were the lenticels of the growing 
tree. 
A lenticel is a lens-shaped rift in the outer bark, 
filled in with a loose mass of cork-cells, which are 
not rectangular, and ranged in rows after the 
