388 BOTANICAL GAZETTE — [JUNE 
The question naturally arose as to the cause of the difference 
in ice content and why ice was absent in the eight species mentioned. 
Since lowering the temperature from—18° C. to—23.5° C. caused 
the appearance of ice in some, it would seem therefore to be simply 
a matter of temperature. But the degree of cold necessary to 
cause the separation of ice is proportional to the force which holds 
the water in the tissue. This in turn depends upon the relative 
proportion of water to cell-wall and protoplasm. We should expect, 
therefore, to find in those buds which are difficult to freeze a smaller 
amount of water than in other buds; also smaller cell-structures, 
since by this latter means the proportion of cell-wall and proto- 
plasm is increased. When cells become smaller it is usually the 
water content that most rapidly diminishes, the protoplasm follow- 
ing at a much lower rate. I have made the following measurements 
of the cells and water content in seven of the species in which there 
was much ice, and in seven in which ice did not appear at —18° C. 
Max. aver. | Min. aver. | Text. of wall | % of water 
mm. mm. 
A. Ice abundant in. bud-scales, leaves, 
nd growing point— 
Crntecwtis: pronttata. << 670.23 625 oss 0.040 0.012 thin 49-4 
RT ENNOS Ste aie ots or een eae Be O51 0.015 : 46.6 
Byrn Vileatigg 6.565. ..55 204 254 0.0045 | 0.009 ot 53-2 
Pee MN id a deh 0 ware 0.021 0.009 : 45-9 
SerNAl, cues ee a 0.021 0.015 ie 47.6 
Populus racine LEP Dee wit 8 = sain to 0.025 0.018 2 39-3 
meuttile lites es 5 vic 0 Pa Sh 0.018 0.006 se 37-5 
B. Ice not sie at — 715" Cc 7 elles 
Querc Pee PN Sa. 3s th elements 0.015 0.006 thick 22-9 
orylus:rostratac: < .0csce 8 oe see: 0.018 0.006 a 29.7 
Castanea dertata. .. 28 igs cds ees 0.018 0.015 = 25.4 
F Westen. co ree ces | 0.008 0.003 26.8 
a aphedia can foe ee ee 0.048 0.015 very thick 31-4 
JUG CUMTOR, 055 65 eo eg oe | o12 0.003 thi ck 25:9 
Fraxinus americana... ..........-;. 0.021 0.003 | 29.8 
Our supposition regarding the smaller size of the cells and 
smaller water-content in the second group, therefore, seems to be 
upheld by these results. 
In the twigs ice is also present in very cold weather, where it 
may be found in three different localities. TThe largest quantity 
occurs in the cortex, where the ice crystallizes in prisms arranged 
