APPENDIX. 267 



temperature rising slowly. This greatly reduces the liability of injury to the 

 plants. Dr. B. T. Galloway, in the United States Department of Agriculture 

 Yearbook, 1895 (p. 145), thus explains why frozen plants are less likely to be 

 injured when warmed slowly: 



''Under the influence of cold, the water in the cells escapes, and may be 

 frozen either in the spaces between the cells or on the surface of the leaf, 

 stem, or whatever the part may be. As the temperature rises, this frozen 

 water may again be taken up by the cells, and in such cases little or no injury 

 results, [f for any reason, however, the cells are not able to regain the 

 water withdrawn by the cold, injury or even death maj- result. In many 

 cases the rapidity with which the ice is thawed has a marked effect on the 

 ability of the cells to gain their normal condition. If the thaw is gradual, 

 the water is furnished no faster than the cells can absorb it, and equilibrium 

 is, therefore, soon restored, the chemical processes which were checked dur- 

 ing the freeze are resumed, and the plant soon regains its normal condition. 

 With a rapid thaw, however, the cells are not able to take up the water as fast 

 as it is furnished, and as a result chemical decomposition sets in, and death 

 follows. Death in this case is essentially the same as that which results from 

 drought. The cell loses water to such an extent that it is not again able to 

 become turgid, and as a result it finally withers and dies." 



Other methods— While the foregoing methods are quite efficacious in i)ve- 

 venting injury, still the expense is entirely too great to admit of their adop- 

 tion for general use in orchards. 



Strawberries and other low plants are frequently protected by covering 

 them with straw or other loose substances. 



Frequently young potato plants are saved by i^lowing a furrow alongside 

 and allowing the dirt to bury them. 



Cranberry growers in the marshes of Wisconsin flood the marshes when 

 frost is expected. In this case the protection is probably due, for the most 

 part, to the high specific heat of w^ater, as only portions of this land are sub- 

 merged. 



Smndge ^tires — Since radiation is so reduced as to prevent the formation of 

 frost on cloudy nights, many have thought that an artificial obscuration of 

 the sky by means of dense smoke would be an excellent means of protection. 

 The efforts of this character which have been made have resulted in decidedly 

 varying success. In the wheat fields of the Dakotas excellent protection was 

 obtained, while the experience of orchardists in Florida and Southern Cali- 

 fornia has not shown such a uniform success. 



Since it was supposed that the protection resulted from the obscuration of 

 the sky by means of smoke, the best protection was expected from the use 

 of that fuel which would produce the greatest smoke. 



In the Dakotas the best and most convenient material at hand was the 

 straw of the previous year's crop, which had been left in the fields all the 

 w^inter and through the rainy spring, until it was quite thoroughh' soaked 

 with water. 



In Southern California and Florida straw was scarce, and where it could 

 be obtained it w-as much drier than that used in the Dakotas, consequently 

 tar, crude petroleum, and other similar smudge materials were substituted ; 



