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1906] WIEGAND—BUDS AND TWIGS IN WINTER 397 
week, during which time temperatures of —23.5° C. had alternated 
with those of 4.3° C., so that the buds were alternately frozen and 
thawed. After removal of the rubber, the tissue appeared as fresh 
and sound as ever; the twigs were then cut and placed with their 
ends in water in the greenhouse, where the treated bud remained 
fresh as long as did others whose scales were freshly removed as 
check experiments.'4 
There exists, it seems to me, insufficient evidence to sustain the 
theory that the exclusion of external moisture has played an impcr- 
tant part in the evolution of scaly buds. 
Heat conduction. 
The popular belief is widespread that bud-scales serve to keep 
out the cold, and indeed such an explanation appears in some of 
our leading textbooks and in various other works. A moment’s 
consideration will convince us that this cannot be true. No plant 
tissue yet known is a perfect non-conductor of heat, or, indeed, less 
than a fairly poor conductor, and scale tissue is no exception; while 
the very thin nature of the scaly covering on some buds, as those of 
Salix, would absolutely preclude their offering more than a moderate 
amount of resistance to the escape of heat. To keep out the cold 
during an entire cold spell in winter would require, even in much 
thicker tissue, an almost absolute non-conductivity, and that is 
possessed by few if any substances in nature, much less by the bud- 
scales. This erroneous impression has arisen probably through 
comparing the action of bud-scales with that of clothing upon the 
human body, forgetting the fact that in the body there is a constant 
source of heat without which clothing could not keep it warm for 
more than a few minutes.'S 
™ Kny found that with the bud-scales and cortex intact average twigs will 
not take up as much water through these organs as they give out in dry air pie ae 
a similar time. He neglected, however, to experiment with naked buds. Ue 
die Aufnahme tropfbar-fliissigen Wassers durch winterlichentlaubte Zweige von 
Holzgewachsen. Ber. Deutsch. Bot. Gesell. 13:361. 1895. 
8 It may be suggested that such a constant source of heat does actually exist 
in a tree, at least so far as the buds are concerned, and that this is provided by the 
heat accompanying respiration. However, reference to any textbook in plant physi- 
ology will show that the amount of heat evolved in this way is but slight in the very 
best examples, which are all herbs, and is mainly evident during the period of most 
