178 MISSOURI BOTANICAL GARDEN. 
constrictions described above. Remembering that most of 
the bands which occur on maple twigs are burst by the twig 
every year (only 1.5-2 per cent are not burst), it seems 
probable that the larger number of bands represented in 
this table would have been burst during the growing period. 
As many of these show that these bands exert radial pres- 
sures running up to 40 atmospheres and more, it seems 
EXCEPTIONALLY STRONG BANDS. 
Tree on which bags | Widthof | Diam. of | Total Breaking Atmospherio 
occurred. band. mm. | twig. mm. | weight. grams. pressure. 
White Pine.... 1.5 1.5 935 83.1 
3 2 2275 75.8 
3 2 2472 82.4 
1 2 650 65.0 
2 1.5 1090 73.7 
MADIG . 6 dt HA 3 3 8202 71.1 
8 3 4324 96.8 
1 2 668 133.6 
2.5 3 8727 100.7 
3 2 8632 121.1 
5 4 1620 162.0 
Sycamiore..... 3 2.5 1778 177.9 
WAUOW 66a 1.5 1.5 1217 108.1 
2.5 ls 2. 8272 130.8 
8.5 3 4737 90.2 
2 1.5 1632 108.8 
2.5 1 1775 158.0 
2 2 2130 106.5 
1.5 1 900 120.0 
2 2 2350 117.0 
4 2 38675 91.9 
TABLE II, 
likely that the pressure which the twigs are capable of 
exerting radially must be at least equivalent to these pres- 
sures in order to burst the bands. It will be remembered 
that the figures which Krabbe obtained, showing that the 
pressure exerted by growing twigs of hard woods was 15 
atmospheres or thereabouts, in no way indicated what the 
upper limit might be. Judging from the structure of the 
wood which he shows, cell division was still taking place 
