406 BOTANICAL GAZETTE [JUNE 
as fresh as others not so treated.'7. The answer to this first question 
then, is, that bud-scales do not function by preventing rapid thawing 
of winter buds; neither does bark so function towards the twigs. 
It has been suggested that bud-scales protect the bud by pre- 
venting rapid radiation from the delicate tissue during the cold 
nights, and thereby preventing a harmfully low fall of temperature. 
MU ier-TuHurGAu,'® by placing one thermometer on some cotton 
under a o.5°!" cloth screen fastened 1°" above the ground, and 
another thermometer outside, was able on a clear night to get 4° C. 
difference due to radiation. Griiss'® states that differences in 
temperature due to radiation may be one or two degrees on cool 
nights just before sunrise, and as great a difference as 6° C. has been 
observed by other investigators. A difference of 4-6° C. would 
frequently be of importance to tender exotic buds in winter, but 
it is scarcely to be supposed that so slight a difference would be 
of much moment to the great majority of perfectly hardy species 
which withstand all of the fluctuations of our vigorous American 
climate without injury. Indeed these species seem capable of 
existing below any atmospheric temperature that has yet occurred 
in this country, as freezing mixture experiments have shown. Besides, 
the structure of buds does not lead one to expect a radiation screen 
as efficient as those specially constructed. Strictly speaking, the ques- 
tion here is not one of radiation of heat, since the scales are all more 
or less in contact, but of conduction, and as such has already been 
treated. 
HENsLow’? has shown that it scems desirable for plants in tem- 
perate regions to protect their delicate bud-structures from loss 
of water when the bud is opening. Such loss he says is favored by 
radiation and heat absorption. The above objection will apply here 
also for the first part of this last statement, and the latter part is 
treated elsewhere in this paper. 
17 Motiscu, H., Untersuchungen iiber das Erfrieren der Pflanzen. Jena. 1897 
18 MULLER-THuRGAU, H., Ueber das Gefrieren und Erfrieren der Pflanzen- 
Landw. Jahrb. 15:563. 1886. 
9 Gruss, Beitrige zur Biologie der Knospe. Pringsh. Jahrb. 23:651. 1891-92. 
20 HENSLOW, G., On vernation and the method of meee of foliage as 
protective against radiation. Jour. Linn. Soc. Bot. 21:624. 1886. 
