jan. i 5> 1921 Freezing vf Fruit Buds 657 



When liquids are cooled to their freezing points, if there be none of 

 the solid material present, they rarely freeze. They may be cooled 

 several degrees further and kept for days without solidification taking 

 place. The introduction of as small an amount of solid as one-hundred- 

 thousandth part of a milligram is sufficient to cause freezing to begin. 

 The smaller the amount of liquid taken the easier it is to superfuse it, 

 and liquids contained in capillary tubes will remain for long periods of 

 time below their freezing point without solidification taking place. The 

 fact that the juice of the buds is confined in small capillary spaces will 

 help to explain in part the unusual hardiness of the buds and the great 

 difference in hardiness of buds that appear to be very similar. This 

 phenomenon explains why they may be cooled below their freezing points 

 and be warmed again without ice separating. 



A classified list of the "danger points," as given by various investiga- 

 tors, is presented in Table I. 



METHODS AND APPARATUS 

 NATURAL FREEZES 



Each spring, for the last seven years, standard minimum thermometers 

 have been placed in especially prepared but simple shelters in fruit trees 

 of various orchards near Logan, Utah, and were read the day after a 

 minimum temperature of 32 ° F. or lower was experienced. A record 

 was made of the yield of fruit of the orchard for the season. The results 

 of this work are found in Table II. 



ARTIFICIAL FREEZES 



The first work consisted in freezing detached branches of fruit buds in 

 the laboratory by means of a specially designed thermostat, the air 

 surrounding the buds being cooled by means of common salt and ice and 

 warmed with an incandescent electric light, which was maintained con- 

 stant at an arbitrarily determined temperature in the usual way with a 

 relay. The extent of the injury was determined by cutting the buds 

 open and counting those that had been damaged and then calculating 

 the percentage that had been frozen. 



Branches of trees were bent down into a vessel surrounded by a 

 second air chamber, the latter being surrounded by a mixture of ice and 

 salt. The minimum temperature was noted, the branch was tagged, 

 and the further development of the buds was observed and the yield of 

 fruit determined. 



This method was modified by having the buds cooled by means of 

 evaporating liquid carbon dioxid instead of using ice and salt. A tank 

 of liquid carbon dioxid was connected to a metal coil that surrounded 

 the bud chamber. The very cold gaseous carbon dioxid cooled the bud 

 chamber, thereby cooling the buds to the desired temperature. 



