AN INDEX OF HARDINESS IN PEACH BUDS 
Earl S. Johnston 
The effect of various environmental conditions on hardiness of the 
peach is an important question to the fruit grower, but a thorough study of 
this subject can not be made until some criterion is found for determining 
the degree of hardiness. A most desirable criterion would be some physical 
or chemical measurement in which personal judgment is reduced to a mini- 
mum. After such a measuring unit has been found it will then be possible 
to determine more accurately the effect of environmental conditions on 
hardiness and the degree of hardiness in different varieties growing under 
the same conditions. 
Ohlweiler,^ Chandler,^ and a number of other workers have found a 
correlation between the density of cell sap and the resistance of the plant to 
low temperatures. In measuring osmotic pressures and freezing point 
lowerings of expressed cell saps a number of important conditions are 
necessarily neglected. The size and shape of cells and the properties of the 
colloids present undoubtedly exert a most important influence. On the 
former depend the size and shape of capillary water films and on the latter 
the amount of water held by imbibition. Both limit the degree of hardiness 
of the tissue. These facts may in part explain the lack of correlation ob- 
served by other workers such as Salmon and Fleming,^ who state that : 
"There appears to be no relation between the cryoscopic value of the 
extracted sap of winter rye, wheat, emmer, barley, and oats grown in the 
field with normal conditions and their ability to resist winter killing. Tur- 
gidityof the tissue as influenced by physiological drought appears to have 
more influence than the kind of grain on the concentration of the cell sap. 
Harris and his co-workers^ have pointed out that the environmental condi- 
tions under which the plant grows seem to modify the osmotic pressure of 
the cell sap." 
^ Ohlweiler, W. W. The relation between the density of cell sap and the freezing points 
of leaves. Rep. Mo. Bot. Gard. 23: 101-131. 1912. 
2 Chandler, W. H. The killing of plant tissue by low temperature. Mo. Agr. Exp. 
Sta. Res. Bull. 8. 1913. 
^ Salmon, S. C, and Fleming, F. L. Relation of the density of cell sap to winter 
hardiness in small grains. Journ. Agr. Res. 13: 497-506. 1918. 
^ Harris, J. A. On the osmotic concentration of the tissue fluids of phanerogamic 
epiphytes. Amer Journ. Bot. 5: 490-506, 1918. Harris, J. A., and Lawrence, J. V., 
with the cooperation of R. A. Gortner. The cryoscopic constants of expressed vegetable 
saps as related to local environmental conditions in the Arizona deserts. Physiol. Res. 2: 
1-49. 19 16. 
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