Grossenbacher—Radial Growth in Trees. 
69 
Fick 139 regarding the action of the enzymes which coagulate 
blood and milk. 
The fact that stems and branches of trees are more pliable and 
easily bent while in the midst of active spring growth than they 
are at any other time, indicates that perhaps some enzymotic 
softening of the mature wood occurs during the period of most 
active growth. The upward bending of a branch on a decapi¬ 
tated conifer also argues for the presence of some softening 
agent during the time of most vigorous growth because of the 
fact that such branches often bend in response to gravity at 
places where lignification had previously occurred. In other 
words, it seems that one of the most important factors in the 
production of large wood cells in spring and smaller ones in 
summer may be the presence of enzymes which retard lignifica¬ 
tion and prevent rapid thickening of the walls and thereby per¬ 
mit growth or hydrostatic pressure to develop large cells in 
spring; while the absence or inactive condition of those enzymes 
induces rapid thickening and early lignification of the walls in 
summer and thus checks the enlargement of summer-wood cells. 
It may be that the idea of growth force expressed by Detlef- 
sen, Mer and others as well as “the impulse to grow” em¬ 
phasized by Morgulis imply the same sort of notion as that ad¬ 
vanced in the above scheme regarding the possible relation of 
enzymes to ring formation, but in any case the hypothesis is 
only a guess based on rather suggestive indirect evidence. Mer’s 
conclusion that the winter rest of the cambium induces its 
greater activity in spring seems to have something in common 
with the outcome of some feeding experiments by Morgulis, to 
the effect that in subjecting salamanders to alternate periods of 
fasting and liberal feeding a greater growth resulted than by 
more frequent and abundant feedings. A theory to account for 
wood rings must also make use of the evidence brought out re¬ 
garding the effect of variations in bark tension both longitudinal 
and transverse, as well as of the influence of the transpiration 
stream as suggested by Hartig and more recently elaborated by 
Jaccard in his discussion of the distribution of radial growth. 
It should be remembered, however, that transpiration is per¬ 
haps greater during the time summer-wood is formed than it is 
while spring wood develops; to say that larger cells are pro¬ 
duced in spring to meet the higher water requirements of the 
approaching summer explains nothing. 
139 Pick, A. Ueber die Wirkungsart der Gerinnungsfermente. Archiv. 
Gesam. Physiol. Mens. Thiere. 45: 293-96. 1889. 
