New YorK AGRICULTURAL EXPERIMENT STATION. 403 
In order to understand the function of any process of bridging 
over a girdle it is necessary to consider the sap flow of woody 
plants. In general it may be said that crude sap after it is taken 
up by the roots passes into the upper portion of the tree or shrub 
through the sapwood; that is, the wood of the last two or three 
years’ growth. After this sap has been elaborated in the leaves 
and returns to build up the plant tissue it is passed almost wholly 
through the phloem or inner bark. When it comes to a point 
where the inner bark has been destroyed it may pass in through 
the sapwood and thus continue downward, but any such passage 
is difficult and slow. In an ordinary girdling, the sapwood, where 
the ascending current of sap passes, is practically uninjured so 
that the upward flow of crude sap is not interfered with to an 
appreciable degree. Hence trees which have been girdled will 
usually leaf out all right in the spring; but the parts below the 
injury not being able to secure any elaborate sap from the leaves 
above, no new roots can be formed and the plant later dies from 
lack of root nourishment. Hence the object of the operation 
described below is to bridge over the injury so that the descending 
stream of sap in the inner bark may pass to that portion of the 
tree below the wound. 
To make such a bridge, first, take a twig, preferably of last 
year’s growth, although this is not necessary, and with a sharp 
knife sharpen this twig to a wedge at both ends as shown in Fig. 
1. This twig should be slightly longer than the distance across 
the wound, measuring up and down the tree, and should be stiff 
enough so that it will not bend easily. Next take a half-inch 
chisel and make an incision in the tree just above the girdle. 
This incision is made with the bevel of the chisel outward and 
the edge extending upward and inward through the bark into the 
wood. A similar incision is made just below the wound and 
directly beneath the first with the edge of the chisel directed 
downward and inward through the bark. Now press one of the 
sharpened ends of the twig firmly into the lower incision and, 
bending the twig, spring the other end into the incision above. 
Such twigs should be placed at intervals of about an inch apart 
as far around the tree as the wound extends. If the incisions 
have been made true and the twigs are just the right length they 
