CONSTRICTION OF TWIGS BY THE BAG WORM. 177 
Concerning the width of the bands, there is more variation. 
Of the 413 bands, 122 were 3 mm. in width, 65 were 2.5 
mm. and 114 were 2 mm., in decreasing numbers of smaller 
and greater widths. The largest number occurring on any 
particular diameter of twig were 3 mm. in width. Prefer- 
ence for the twigs 3 mm. in diameter is furthermore shown 
on Diagram 2, a, representing the relation of strength, 
using the twigs of different widths as the variable, and 
Diagram 2, b, where the bands of different widths are 
used as thevariable. The final results obtained with bands 
taken from maple twigs are plotted in Diagram 1; the 
figures at the bottom of the table indicate the number of 
atmospheres pressure exerted by any band upon the particu- 
lar twig which it subtended. The figures at the left of the 
table represent the numbers of individua] bands exerting 
any particular number of atmospheres pressure. There 
were, as may be seen from this, four bands which 
exerted a pressure of 10 atmospheres and 16 which 
exerted a pressure of 19 atmospheres each, etc. While 
the number of bands which were broken was a rather small 
one for the purpose of any definite statistical study, 
enough were tested, nevertheless, to show a number of in- 
teresting facts. The radial pressure exerted by the bands 
varied from 4 atmospheres to 162 atmospheres in the case 
of the maple. The greatest number of the bands varied 
between 14 and 44 atmospheres. The strength which 
some bands showed was surprising. On Table II a num- 
ber of instances of extreme strength are shown for maple 
and other trees. The deductions which may be made in a 
tentative way from the results shown in Diagram 1 are as 
follows: A great variation in the pressures exerted by the 
bands of the bag worm on the twigs of maple trees exists. 
Some of these pressures are very great, and it is probable 
that bands like those which showed pressures of 102 to 162 
atmospheres are the ones which are responsible for the 
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