46 THE REPORT OF THE No. 36 



puting calendars and tables which aid very much in the computation of phenologi- 

 cal dates. 



Dr. Hopkins informs us that the rates of variation in the dates of periodic 

 events were determined earlier by Schubler in 1830 for the distance between Parma, 

 Italy, and Greifswald, Prussia, as 4 days for a difference of about 325 feet of 

 altitude and 1 degree of latitude. Although Quetelet, in 1846, was aware of the 

 influence of longitude, it remained for Fritsch, in 1865, to state that each degree 

 of longitude westward made a variation of 4/10 of a day. In 1893 Ihne found 

 the variation to be about 9/10 of a day. Dr. Hopkins, in 1900, concluded from 

 his investigations in West Virginia that the rate of variation was 4 days to 1 degree 

 of latitude and 400 feet of altitude, and later in 1915 concluded that there was a 

 variation of 4 days to 5 degrees of longitude. 



The Bioclimatic Law. The Bioclimatic Law may be stated as follows: 

 The variation in the time in which periodical events occur in the seasonal develop- 

 ment and habits of plants and animals at different geographical positions within 

 the range of their distribution is, other things being equal, at the rate of four days 

 for each degree of latitude, five degrees of longitude, or JfOO feet of altitude. 



According to this law, lines running from the east toward,^ the north-west 

 at the rate of one degree of latitude to five degrees of longitude represent the same 

 constant or average date of periodical phenomenon for any given level throuohout 

 their length. Such lines are called isophanal lines, and in accordance with this 

 law Dr. Hopkins has constructed isophanal maps of the United States (Fig. 1). 

 Meridian lines drawn at right angles to the isophanal lines are called phenological 

 meridians. 



The influence of certain local factors that modify the average dates of the 

 periodic phenomena for each quadrangle, such as topography, lakes, large rivers, 

 rainfall, sunshine, etc., according to their intensity, is marked on each quadrangle 

 as plus (later) or minus (earlier) departures for both spring and autumn (Fig. 3). 



Dr. Hopkins believes that the amount of departure of the actual from the 

 computed date for any locality represents the Intensity of the action of local factors. 



For example, in Florida the departures are ten days earlier than computed 

 time for autumn and ten days later for spring events; for Western Ontario only 

 nine days later for autumn. Such departures were based on a study of more than 

 40,000 reports on the date wheat harvest begins. 



The departure constants were obtained by establishing phenological bases or 

 '' localities where a sufficient number of observations have been made to establish 

 corrections for local and regional influences, so that the date of any seasonal event 

 recorded there may serve as a reliable basis for the computation of corresponding 

 dates for the same event at any other geographical position within the same or 

 different regions of a country or continent." 



Wooster, Ohio, was taken as the base for fall wheat seeding on account of the 

 thorough work done there by Webster in connection with the determination of 

 Hessian fly-free dates, while Minnesota was taken as the base for spring wheat 

 seeding. 



In accordance with the law and with the amount of departures for different 

 localities Dr. Hopkins, in 1917, proposed to the U. S. Department of Agricul- 

 ture to make wheat seeding map-calendars for all the States for the purpose of 

 increasing the wheat yields for 1918 by the control of the Hes-ian Fly. On 

 account of the limited time, however, posters with maps and instructions were 

 prepared for only New York, Pennsylvania, Illinois, Indiana, Nebraska, New 



