64 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Recent studies of methods for making more definite minimum- 

 temperature forecasts, based on mathematical hygrometric and ther- 

 mometric formulae, have proved very helpful, and these studies will 

 be continued. These local officials are studjdng the topographic and 

 other conditions, and give expert information to those orchardists 

 who are prepared to prevent frost damage by artificial means. 



Special frost warnings are also distributed from a large number 

 of Weather Bureau stations for fruit and truck interests, althougli 

 no special station reports may be received. 



ARTIFICIAL PROTECTION OF ORCHARDS, GARDENS, ETC.. FROM FROST. 



The service described in the preceding section has been maintained 

 for many years. Beginning with the fiscal year Jul}'- 1, 1917, Con- 

 gress made available a special appropriation for the study of the 

 efficiency of methods of artificially protecting orchards, gardens, etc. 

 Preliminary preparations for the inauguration of this work were 

 begun before the close of the year, in order to take advantage of the 

 spring frosts of that season, and the work will be carried forward 

 during the year with the appropriation available. 



FROST AND TEMPERATURE STUDIES IN NORTH CAROLINA. 



In 1912 the liureau inaugurated a study of the very interesting 

 atmospheric phenomena and anomalous climatic features which have 

 been designated thermal or frostless belts and verdant zones, and 

 which are strikingly developed in some of the mountainous sections 

 of western North Carolina. 



The observational program of this project was brought to a com- 

 pletion December 31, 1916, with nearly five years of accumulated data 

 from about 68 stations. 



This project has been supervised by Prof. H. J. Cox, who is now 

 engaged in the completion of his report, which will doubtless supply 

 a much more comprehensive and detailed account of these climatic 

 phenomena than ever heretofore attempted. 



ALFALFA SEED-WARNING SERVICE. 



A minimum-temperature forecast service is maintained at Salt 

 Lake City, Utah, for the benefit of the alfalfa seed growers in central 

 Utah. Four special reporting stations are in operation and the in- 

 formation from these is used as an aid in making the minimum tem- 

 perature predictions. The plan of the seed gi'owers is to leave their 

 last stand of alfalfa for seed ; if freezing temperature occurs while 

 the matured or nearly matured plants are standing the seed is ruined; 

 if the warning can be received a sufficient time in advance to cut the 

 alfalfa, only the top layer will be damaged. The gi'owers frequently 

 run their mowing machines all night long preceding a dangerous 

 temperature. 



A similar service has been put into operation during the present 

 season in western South Dakota, with Rapid City as the distributing 

 point. No special stations have yet been established, however. This 

 service is susceptible of expansion. 



