OCTOBEE 10, 1919] 



SCIENCE 



351 



erally considered as the temperature at whicli 

 most plant growth begins in spring and ends 

 in fall, Mr. Kineer made maps showing the 

 advance and retreat of the isotherm of 43° I", 

 in the United States in spring and fall and 

 of the length of the period between the date 

 in spring when the normal mean daily tem- 

 perature rises above 43° F. in spring and falls 

 below it in autumn. This period he called 

 the " vegetative period." These maps were 

 then compared with the corresponding maps 

 of last killing frost in spring, first killing 

 frost in autumn and average length of the 

 growing season (i. e., between killing frosts) ; 

 and other maps were made to show the differ- 

 ences, which amount to about ten days in the 

 iN'orth and thirty or more in the South, the 

 vegetative period being the longer. Other 

 maps show that the normal mean daily tem- 

 perature on the average frost dates just men- 

 tioned are for most of the country between 

 50° and 57° F.; on the Great Lakes, the 

 Pacific, and the Atlantic north of Hatteras, 

 however, the corresponding temperatures are 

 below 50° F. Mr. Kineer points out that pro- 

 tective measures against frost damage may be 

 well worth while in the South, where the 

 vegetative period usually continues for weeks 

 after the first killing frost, but not in the 

 North, where, in autumn for example, low 

 temperatures would soon stop the gi'owth of 

 vegetation which might have been protected 

 from the first killing frost. 



Temperature Influence on Planting and 

 Harvest dates (by J. B. Kineer, 3Io. Weather 

 Review, May, 1919, Vol. 47, pp. 312-323, 20 

 figs., inclu. maps). — This is based largely on 

 a study of the maps in " A Graphic Summary 

 of Seasonal Work on Farm Crops,"*^ in com- 

 parison with temperature data. 



It is suggested that the mean temperature at 

 wMeh planting of a given crop can be aecom- 

 plished be used as a base, or starting point, for any 

 method that may be employed for temperature 

 s umm ation, instead of a general base for all crops 

 (e. g., 6° C). . . . Spring wheat seeding usually 

 begins . . . when the normal daily temperature 

 rises to 37° or 40° F. The corresponding tempera- 

 ture for spring oats is 43°, for early potatoes, 45°, 

 for corn 55° and for cotton 62° P. Cotton and 



corn are warm-weather crops and the areas in 

 which successful production on a commercial scale 

 can be accomplished are limited principally by 

 both the general temperature conditions and the 

 temperature at which planting may be accom- 

 plished. There is a close relation between spring 

 temperatures and the condition of these crops to 

 certain dates in the early stages of growth. 



Alfalfa Say and Seed Oroiving in South 

 Dakota and Utah (separate papers by H. W. 

 Johnson of Eapid City, S. Dak., and J. 0. 

 Alter of Salt Lake City, Mo. Weather Bev., 

 May, 1919, Vol. 47, pp. 328-332, 5 figs.).— 

 " Alfalfa seed is usually produced [in S. Dak.] 

 when conditions are such as to retard the 

 maturing of the first hay crop, and then in 

 paying quantities only when there is a com- 

 parative shortage in the moisture supply, 

 hence the weather conditions determine 

 whether the second crop shall be cut for hay 

 or left for seed. If there is considerable rain- 

 fall, the second crop is usually cut for hay, 

 and a third crop is frequently iwssible." As 

 rainfall conditions fluctuate widely on the 

 Great Plains, the western South Dakota 

 alfalfa farmer has in such an arrangement a 

 fine insurance against drought or unusual 

 amounts of rainfall. In Utah the seed-crop, 

 which follows a cutting for hay, needs special 

 weather conditions for the best yields: there 

 should be 



sufficient moisture during its early growth to pro- 

 duce a vigorous, healthy plant, but the weather 

 should be dry and not too warm while the plants 

 are in bloom. The dry spell must not be too ex- 

 tended, however, as the seed must have sufficient 

 moisture while setting to give it size and weight. 

 It takes nearly twice as long to grow and mature 

 a seed crop as it does a hay crop. As the seed crop 

 is not always ripe on the occasion of the first 

 killing frost in fall, considerable importance Is at- 

 tached to frost and minimum temperature fore- 

 casts. On the receipt of frost warnings, the 

 usual practise is to cut as large an area as possible; 

 but as the first cold period is often followed by 

 several weeks of fine ripening weather, and as the 

 value of the seed is said to increase at the rate of 

 nearly $5 an acre each 24 hours when ripening, 

 efforts should be made to protect the plants from 

 frost damage without cutting. 



Ch.^rles F. Brooks 



■Washington, D. C. 



