384 Pinna ‘BOTANICAL GAZETTE [JUNE 
most cases dark, and artificial darkening, when unaccompanied 
by deleterious factors, seems to accelerate the opening. 
PHYSICAL CONDITIONS IN FROZEN BUDS AND TWIGS. 
From many inquiries it would seem that very few people are 
really sure. whether free ice is actually present in buds in winter. 
Nevertheless, this is one of the most common phenomena connected 
with the winter condition of trees and shrubs. To put the matter 
on a firm basis of observation I undertook, during the winter of 
tgo1, to section buds of various trees during cold pericds and to 
determine under the microscope the amount of ice present. The 
method employed was as follows. Early in the morning, at about 
sunrise, after a fall of temperature to —18° C. or below, a table, 
microscope, razor, needles, slides, and cover glasses were placed 
in a shady situation in the open air, where they were allowed to 
become thoroughly cooled. Free-hand cross sections of the various 
buds were then made, and mounted on the slide. For a mounting 
medium cedar-wood oil was found best. A small quantity of this 
in a vial was allowed to cool with the instruments. One important 
advantage in the use cf cedar-wood oil over those of a denser nature 
lay in the fact that it did not congeal at the low temperatures of 
the experiment. The ice remained unmelted in the preparation 
and could be observed at leisure; or if the thawing process was 
under study the slide could be carried to a warm room and placed 
under another microscope. The melting ice was unable to evapo- 
rate from the section, and therefore it was easy to determine whether 
the water was all reabsorbed, and the approximate rate of absorp- 
tion. 
The ice was found to occur always in broad prismatic crystals 
arranged perpendicular to the excreting surface; and usually formed 
a single continuous layer throughout the mesophyll of the scale or 
leaf, to accommodate which the cells were often separated to a con- 
siderable distance (figs. 2, 3, 4). This ice sheet was composed of 
either one or two layers of the prismatic crystals, depending on the 
water content of the adjacent surfaces, and was often as thick as the 
whole normal scale. The cells surrounding the ice, having lost their 
water content, were in a more or less complete state of collapse, 
