METEOROLOGY — WATER. 315 



generator as ammonium snlpbate. Nitrates also were found to exert a decided 

 decomiwsiug action on liydrocj'anic acid, but tlie amount was mucli less than 

 tliat produced by chlorids. In view of the important bearing of the sodium 

 chlorid content, an analysis of a cyanid is regarded as of little value in fumi- 

 gation work unless the chlorin content is also determined. 



METEOROLOGY— WATER. 



Frost data of the United States, and length of the crop-growing season, 

 P. C. Day (C7. S. Dept. Agr., Weather Bur. Bui. V, pp. 5, eharts .5).— Data 

 from observations made in the open country at approximately 1,000 of the co- 

 operative stations of the Weather Bureau having the longest record, usually 

 from about 10 to 30 years, are summarized in a series of charts showing (1) the 

 average date of the last killing frost in spring, (2) the average date of the first 

 killing frost in autumn, (3) the latest date on which a killing frost has oc- 

 curred in spring, (4) the earliest date on which a killing frost has occurred 

 in autumn, and (5) the average length of the crop-growing season; that is, the 

 number of days between the average date of the last killing frost in spring and 

 the average date of the first killing frost in autumn. 



The imiwrtance of frost statistics is pointed out and the influence of special 

 conditions on frost formation as indicated by these charts is discussed. 



" In the elevated mountain districts and on some of the higher plateaus of 

 the western country freezing temperatures are liable to occur in all months of 

 the summer, but their effect on vegetation is not so pronounced as in the dis- 

 tricts east of the mountains. 



" Cool nights are a feature of all arid regions, due to the intense radiation 

 made possible by the generally clear skies and the lack of moisture in the 

 atmosphere. As a result of these conditions the temperature in the early 

 morning hours may frequently reach the freeznig point but its continuance may 

 not be for a length of time sufficient to injure the plant structure; in fact, 

 owing to the dryness of the air, frost does not always form with a temperature 

 of 32° or even several degrees lower, and in addition plant life subjected to 

 such variations in temperature becomes more hardy and lower temperatures 

 are required to cause serious injury. On the other hand, in the more humid 

 regions the radiation at night is less rapid, the nights as a rule are not so 

 markedly cold, plant life is less hardy, frost forms readily at the freezing point, 

 the same degree of cold is often protracted over much longer periods of time, 

 and vegetation is therefore more seriously affected. 



" Throughout the entire mountain and plateau regions there are protected 

 valleys and slopes where the influence of topography on air drainage is sufficient 

 to considerably modify the effect of latitude in the distribution of tempera- 

 ture, and plants and fruits native to localities much farther south may be grown 

 with little fear of injury from frost. There are also localities where on account 

 of the drainage of air from high, snow-covered mountains frosts are more liable 

 to occur than in other localities in the same latitude not so exposed. 



" Consideration of these points is essential to the successful locating of sites 

 for orchards and gardens in all hilly and mountainous regions, it being pos- 

 sible to find belts on the sides of mountains or high hills where plant growth 

 begins several weeks earlier in the spring than at the tops of the hills or In the 

 valleys below; and likewise in autumn frosts are delayed to the same extent, 

 thus lengthening the crop-growing season in these belts several weeks. 



•' The iiifiuence of large bodies of water also in tempering the severity of frosts 

 is clearly brought out iu these charts, particular atteatiou being invited to the 



