404 BOTANICAL GAZETTE [JUNE 
that the readings might be different if radiated instead of direct 
heat was employed, especially since there is a considerable difference 
in the nature of such heat, as shown by the well-known fact that 
direct heat from the sun passes easily through glass into the green- 
house, but when radiated passes out with much greater difficulty, 
thereby warming the house. 
A number of readings taken with naked and_ horsechestnut 
bulbs transferred from the shade to the surface of a black book in 
direct sunlight with the bulb raised 3-4™™, or with the bulbs pro- 
jecting several inches over the edge of the book which itself was 
raised several feet from the ground, or with the bulbs raised 7.5—10°™ 
above the surface of the book, showed no appreciable difference 
that could be referred to a difference in kind of radiated heat. There 
was some difference in the readings, of course, but this could ke 
traced directly to the fact that there was more intense heat where 
the heat of radiation was also present. In case of more intense 
heat the extra absorbing power of the bud-scales was at first more 
obscured by the slightly greater retardation of heat-penetration due 
to the greater difference in outside and inside temperatures, as we 
should expect from the deductions from Tables III and IV. This 
was partially shown by the difference in locality of the crossing 
of the two curves plotted from each reading. 
Looking at the matter from still another standpoint, we may 
consider how much time is required for a bud to thaw. As shown 
by the cover glass measurer, the wrinkled willow twigs thawed and 
became perfectly normal in thirty minutes at the temperature of 
the laboratory. Undoubtedly the ice had disappeared in about 
half the time. Large buds of horsechestnut will lose all their ice 
in about twenty-five minutes under similar conditions, and buds 
of Negundo in about fifteen minutes. The small buds of the black 
cherry require only about ten minutes for thawing. The time 
required in the laboratory for the various buds, therefore, is ten 
to thirty minutes. The question is whether when the temperature 
changes are slow the buds thaw proportionately more slowly. The 
answer must be that they will, slightly, just as a cake of ice will 
thaw more slowly when the temperature rises gradually than when 
the rise is abrupt. This difference is proportional to the size of the 
