4 
170 MISSOURI BOTANICAL GARDEN. 
dently entirely cut off, and as a result practically no 
growth takes place in the twig on the side below the bands. 
The portion of the twig above the band continues to grow 
for a considerable period. The absolute cessation of the 
passage of starch and other substances from the leaves 
towards the trunk is well shown by the total absence of 
starch in the region below the band in the fall of the year, 
while in the region above the band the wood parenchyma 
and bark cells are completely filled with starch. In the 
hardwood trees the pressure of the band is evidently never 
great enough to entirely obstruct the passage of elaborated 
materials. No cases were found in the large number ex- 
amined, with the exception of the locust, where the con- 
striction caused by the band was great enough to prevent 
the growth of the part below it. In the fall of the year 
starch is found in the parenchymatous tissue both above 
and below the band in almost equal quantity. The differ- 
ence in the behavior of the conifers and the hard woods 
is a suggestive one, as indicating the greater adaptability 
of the latter, and their higher grade of physiological organ- 
ization. 
GROWTH ENERGY OF TWIGS AS INDICATED BY THE PRES- 
SURE OF THE BANDS. 
It has been stated that in the normal course of events 
the twigs burst the bands of the bag worm shortly after 
the beginning of the period of wood formation in the early 
summer of the second year. Now and then the strength of 
a band was such, however, that the twig failed to burst it, 
and as a result the constrictions just described were formed. 
The bursting of the bands has been explained as due to the 
force exerted by the twig after it began to grow in 
diameter. Putting it in another way, the bursting of the 
band may be said to be due to the growth energy developed 
by the growing twig. That plants do exert a certain 
amount of growth energy is a familiar fact. It is well 
known how the roots of trees will lift the flagstones in the 
