234 POMOLOGY 



oak leaves are the size of squirrels' ears" is familiar. Others 

 use the time of the arrival or migration of certain birds, the 

 unfolding of the leaves or flowering of certain plants, or the 

 appearance of certain insects as an index to farm and or- 

 chard practice. Such a method, if well observed, should 

 be a veiy accurate guide, as it represents the sum of all the 

 complex factors involved and no instrument can do this. 

 206. Bioclimatic law of latitude, longitude, and altitude.^ — 

 A large number of observations made at many points 

 and over a period of years has resulted in the deduc- 

 tion of a set of laws in regard to the response of plant 

 and animal life to climate. Howard reports the following 

 laws: 



1. The periodical phenomena of plants and animals are 

 in response to the influence of all the complex factors and 

 elements of the climate as controlled, primarily, by the mo- 

 tions of the earth and its position relative to the influences 

 of solar radiation. 



2. The variations in the climate and consequent varia- 

 tions in the geographical distribution and periodical activi- 

 ties of the plants and animals of a continent are controlled 

 by the modifying influences of topography, oceans, lakes, 

 large rivers, and of other regional and local conditions, and 

 the amount and character of daylight, sunshine, rain, snow, 

 humidity, and other elements and factors of a general and 

 local nature. 



3. There is a tendency toward a constant rate of variation 

 in the climatic and biological conditions of a continent as a 

 whole in direct proportion to variation in geographical posi- 

 tion as defined by the three geographical coordinates, lati- 

 tude, longitude, and altitude. 



lU. S. Dept. Agr. Monthly Weather Review. Suppl. No. 9, 1918. 

 A. D. Hopkins. Periodical events and natural law as guides to agricul- 

 tural research and practice. 



