44 THE IJEFUirr OF TtlE N... 36 



The Science of Phenology. From time immemorial agricultural })raetice 

 has been guided by meteorological factors. Primitive man, no doubt, soon dis- 

 covered that his food plants required a limited period to reach maturity and that 

 every growing season had its earliest and latest dates for j^lanting. He soon 

 learned, too, that these dates varied with different regions, with different seasons, 

 and with local weather conditions. In the course of tinle a mass of observations 

 accumulated, which constituted the basis of farm practice. Naturally much error 

 crept into the observations and false deductions were drawn from certain co- 

 incidences, but on the whole the early growers of plants were guided by experience. 

 Their contact with nature was very intimate, perhaps more intimate than that 

 of the farmers of to-day. They knew the times of opening of the buds of the various 

 shrubs and trees, and of the arrival and departure of the birds, and learned to 

 associate certain farm practices with these events as natural guides. 



For example, the time of the appearance of the lilossoms on the maple was 

 considered by many people a suitable time to begin gardening ; the blossoming 

 of blackberries the best time for bean planting; the blooming of the locust trees for 

 the planting of cotton ; the mouse-ear size of white oak or maple leaves for the 

 planting of corn ; the opening of the elder flowers for the sowing of turnip seed : 

 the ripening of the elder berries for the harvesting of the early onions ; and the 

 ripening of the burs of the small cockle-bur for the harvesting of the late crops. 

 In other words, the early farmers associated their farming operations with periodic 

 phenomena connected with some tree, shrub or plant. 



In the eighteenth century when plants began to be studied scientifically 

 attention was given to the recording of oliservations on such periodic phenomena 

 as the opening of the buds, the time of flowering, the ripening of the seeds, etc., 

 which give rise to the science of phenology. At the same time studies were made 

 to determine the geographical distribution of plants and animals. 



In the course of these investigations the rates of variation in the dates were 

 partially determined for different latitude, longitude and altitude, but the number 

 of data was not sufficient to permit a definite law of variation to be formulated. 



It Avas early observed that while temperature was the main controlling factor 

 in bringing about variations in periodic phenomena other faotors also played an 

 important part. Dr. Merriam's maps of the zonal distribution of plants and 

 animals into Life Zones were largely based on the temperature factor and are very 

 suggestive and helpful in matters of life distribution. These mai^s, however, dr 

 not furnish information regarding the dates of periodic phenomena in different 

 regions and districts so much desired by the economic biologist in the matter of 

 application of methods of control in the different regions. 



As an example, the old spr%'ing calendars, based on regional distriljution 

 rather than phenological phenomena, have lieen discarded as unsatisfactory, and 

 instead " some periodic event in the plant to which the spray is to be applied 

 is given as the index to the time to do the work." 



Dr. A. D. Hopkins was the first person in America, I believe, who attempted 

 to apply this science of phenology to the solution of entomological problems, 

 especially those relating to certain forest insects in West Virginia. Later it was 

 applied in connection with the control of the Hessian Fly, and as an outcome of 

 the investigations a definite Bioclimatic Law was formulated, which forms a work- 

 ing guide for farm practice and biological research over the entire continent. In 

 connection with this law Dr. Hopkins has prepared a system of ma])s and com- 



