1906] WIEGAND—BUDS AND TWIGS IN WINTER 389 
in single or double series according to the law of freezing tissues. 
The ice is more frequently in the form of a continuous ring, or really 
a cylinder, extending entirely around the twig, prying apart the 
cells of the cortex in which it lies. The outer cylinder of cortex 
in such twigs is completely separated from the inner layers when 
frozen. In a few species instead of the continuous layer, lens- 
shaped ice masses are interpolated irregularly throughout the cortex. 
The cortical cells after the withdrawal of the water are as com- 
pletely collapsed as were those in the bud scales, but they also 
usually regain their normal condition on thawing. In the wood 
ice rarely forms in large quantities. It is usually confined to small 
masses in the vessels themselves, or, according to some authors," 
sometimes extends in radial plates in the pith rays. In sectioning 
twigs, I myself have never seen ice in the wood elsewhere than in 
the vessels or wood-cells. In the pith the ice, so far as I have been 
able to observe, always occurs within the cells and therefore in very 
small masses. 
At the time when the buds were sectioned, cross-sections of the 
twigs were made and mounted in the same manner. Ice was 
found in the cortex of all those in which it was present in the bud, 
but usually in proportionately larger quantities. It was also found 
in the following species which showed no ice in the buds: Corylus 
rostrata, a small amount in large clefts in the cortex; Castanea 
dentata, some ice in ordinary small spaces of the cortex but not 
aggregated; Hamamelis virginiana, a ring of ice completely around 
the stem in young twigs. In Fraxinus, Fagus, and Juglans none 
could be found, and Quercus was not investigated. 
Since water on freezing increases in volume, one would at first 
thought expect the frozen twigs to be larger in diameter than normal. 
Such, however, is not the case. In every instance a distinct con- 
traction occurred, which in some cases was very marked.*? 
_ ™ MULLER-Tuurcau found ice present in the large vessels of Syringa, Cornus, 
and in pears, almost completely filling them; and several times he could also dem 
onstrate it in the wood-cells. The ice was the most distinct, however, in the vessels 
of the grape. Ueber das Gefrieren und Erfrieren der Pflanzen. II. Landw. Jahrb. 
™2 Both Sacas and MU@LLER-TuuRGAU have shown that a similar contraction 
occurs quite generally when herbaceous tissues freeze. SACHS, J., Krystallbildung 
