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166 MISSOURI BOTANICAL GARDEN, 
one case with rollers acting for a short period and rapidly 
applied, while in the case of Kiister’s unions it started as 
a slight pressure and, increasing to a maximum, continued 
for a long period of years until a pressure of 11-17 atmos- 
pheres was reached. Kiister furthermore calls attention to 
the change in direction of growth of the cambial cells, which 
normally form woody cells with their long axes parallel to 
the axis of the stem, but which under the influence of the 
pressure change their direction 90 degrees, many of them 
being curved and bent into **C”’ and‘*S”’ forms. He 
regards these as originating from bent and displaced cam- 
bial cells; their formation being a physical process, and 
their displacement probably due to the pressure coming 
only from one side, which gives these cells an opportunity 
for lateral development. 
In the case of the bands of the bag worm, the pressure 
applied was very similar to that obtained in the investiga- 
tions of Krabbe, with the exception that the force was ap- 
plied gradually, and in that manner was more like the 
pressure obtained by Kiister when he caused two branches 
to join by being pressed together at one side. From the 
description of the changes which take place in hardwood 
trees particularly, under the influence of the constriction 
caused by the bands of the bag worm, it will be noted that 
these changes are almost identical with those described by 
Krabbe. In no case is there any evidence of the formation 
of the parenchymatous tissue spoken of by Kiister. Ex- 
amination of branches of maple, sycamore, red gum, wil- 
low, and other hardwoods, showed that in every case, in 
spite of the enormous pressures that were exerted by the 
band towards the latter part of the growing season, there 
was no cessation on the part of the cambium in the for- 
mation of typical wood cells, though the last cells formed 
were very much smaller, just as were those found by 
Krabbe under his rollers (pl. 25 and 26). I am inclined 
to agree with Krabbe that the pressure does not in any 
