160 MISSOURI BOTANICAL GARDEN. 
beyond the constriction continue to grow normally. The 
new wood formed above the band differs but little from 
the normal type; the tracheids are somewhat shorter than 
the normal ones, but the chief difference lies in their 
manner of arrangement, for a complete turning takes 
place in their position. Instead of growing longitudinally 
‘they grow at right angles to the long axis of the twig. In 
other words, in the region of the swelling all wood fibers 
formed during the first year under the constriction extend 
around the twig instead of longitudinally. In the arbor 
vitae the normal direction of the wood fiber is rarely re- . 
established except in such twigs as are growing vigorously, 
because before a resumption of normal growth is possible 
the twigs usually die. Where the development of the swell- 
ing is very large, a decided buckling of the cells of the 
dick frequently takes place. . 
An examination made of a two-year-old constriction in 
the latter part of the summer, shows the presence of very 
large amounts of starch in the bark, medullary rays and 
pith ring in the part above the constriction, while there 
is practically none in the part below it. An inch or more 
below the constriction no starch whatever occurs. 
The changes which take place in hardwoods differ very 
materially from those just described for the arbor vitae. 
In the spring or early summer following the constriction, 
both the wood and bark continue to 
form under the band, both above and 
below it. Figure 2 represents an 
early stage in a maple constriction. 
After a month or more the wood cells 
<7j appear as if constricted immediately 
under the band. A diversion of the 
wood cells from their normal longitu- 
dinal direction to one at right angles 
takes place in the sycamore, maple 
2. SOFT MAPLE. and other hard woods very much as it 
