CONSTRICTION OF TWIGS BY THE BAG WORM. 179 
with considerable activity under the bands weighted so as 
to exert a pressure of 15 atmospheres, and Krabbe states 
distinctly that the growth energy must therefore be equiv- 
alent to at least 15 atmospheres. As a result of the few 
tests herein described, I am inclined to the belief that the 
pressures are probably very much higher than 15 atmos- 
pheres. Owing to the variability of the bands it does not 
seem practicable, particularly with the small number of 
bands tested and in the absence of determinations as to 
their thickness, to place any absolute value upon the 
growth energy as determined by the bands. That the 
growth energy exceeds 15 atmospheres seems very prob- 
able, and I am inclined to the belief that it may reach the 
extent of 30 to 40 atmospheres, and possibly more. Asa 
matter of statistical interest, Diagram 2, a and b, is added. 
The upper diagram (a) shows the relation between the 
strength of bands of different width, andthe lower one (b) 
the relation between the strength of bands found on twigs 
of different diameters. Both of these tables show that the 
bands of greatest strength are those that are attached to 
twigs of 3 mm. in diameter. 
BIBLIOGRAPHY. 
1. Czapek, Fr. Uber die Leitungswege der organischen 
Baustoffe im Pflanzenkérper. (Sitzungsber. d. Kais. Akad. 
d. Wiss. zu Wien, Math. Naturw. Cl. 106:117. 1897). 
2. Czapek, Fr. Zur Physiologie des Leptoms der Angi- 
ospermen. (Ber. d. D. Bot. Ges. 15:124. 1897). 
3. Fischer, A. Beitrige zur Physiologie der Holzge- 
wichse. (Pringsh. Jahrb. f. Wiss. Bot. 22: 73. 1891). 
4. Friedrich, Josef. Uber den Einfluss der Witterung 
auf den Baumzuwachs. (Mitth. aus d. Forst. Versuchs- 
wesen Oesterreichs. 22 :1897.— Ref., Bot. Zg. 55 : 368. 
1897). 
5. Krabbe,G. Uber die Beziehungen der Rindenspan- 
