614 EXPERIMENT STATION RECORD. 



METEOROLOGY— WATER. 



Meteorological observations in connection with botanical geography, 

 agriculture, and forestry, R. Zon (Mo. Weather Rev., 42 {1914), ^0. 4, pp. 

 217-223, fig. 1). — This article shows how present meteorological observations on 

 temperature, pressure, precipitation, humidity, and wind movement may be 

 regrouped and classified so as to be more useful in the study of plant growth, 

 indicating at the same time certain other observations, especially on soil tem- 

 perature and moisture, which may be utilized for the same purpose. 



It is stated that in order " properly to understand plant life it is essential 

 to group temperature data by periods of growth and rest." A map is given 

 showing the vegetal regions of the United States based on such periods and 

 deduced from the mean monthly temperature for 685 Weather Bureau sta- 

 tions. It is suggested that temperature data should also be grouped with 

 reference to periods of snow cover and to the direction of the wind. 



" The method of computing average temperatures, or the summing up of 

 tempei'atures for different species of plants separately." is considered of little 

 practical value to the biologist. It is more important to distinguish groups 

 of days with a given range of temperature. A classification based on this idea 

 is outlined. The importance of observations on soil temperature and humidity 

 of the air is recognized, but no classification of such data is attempted. 



As regards precipitation, it is suggested that " it will be well to compute the 

 number of days with considerable precipitation in per cent of the total number 

 of days of observation in general, as well as specifically, for winds of different 

 direction. . . . Detailed information concerning the snow cover is especially 

 instructive at the time of its appearance and disappearance. ... It would be 

 of great advantage to students of plant life if [soil moisture] determinations 

 could be made at agricultural and forest experiment stations. . . . 



" Some simple sunshine record, especially for winds of different directions, is 

 also necessary. The occurrence of days with sunshine should be given in per 

 cent of the total number of observations. 



"Air pressure has no direct bearing upon plant life, except that its observatiou 

 often makes it possible to forecast changes of importance to agriculture." 



In conclusion the author points out that, " with the exception of the records 

 of soil humidity and soil temperature, the system of meteorological observa- 

 tions outlined can be carried out with the data which are regularly obtained 

 by our weather stations." 



Period of safe plant growth in Maryland and Delaware, O. T.. Fassig {Mo. 

 Weather Rev., 42 {1914), ^^0. 3, pp. 152-158. pi. 1, flgs. 8; ah.<i. in Bui. Amer. 

 Geogr. Soc, 46 {1914), ^0. 8, pp. 587-590, fig. i).— The frostless period in these 

 States was determined from data obtained from all meteorological stations in 

 the States having a record covering a period of 10 years or more. 



Records at fifty stations covering an average period of 20 years " show that 

 the frostless period, based on the observations of a temperature of .32° F.. is 

 about 10 days longer than the period based on the occurrence of killing frosts. 

 This relation holds good in general for stations in open, level places, but ap- 

 parently does not hold for stations in the mountain districts, where the period 

 based on the occurrence of frosts is longer than that determined from a recoi'd 

 ot freezing temperatures in a shelter 5 ft. above the ground." 



Along the shores of the Chesapeake Bay and the Atlantic Ocean the average 

 period of safe plant growth is shown to be about 210 days, but rapidly decreases 

 with increasing distance from the water's edge. On the western side of the 

 Blue Ridge Mountains and in the lower levels of the Cumberland Valley the 

 period is about ICO days, while on the eastern side of the mountains the period 



