18 



THE HISTORY OF ECOLOGY 



history of insects, Reaumur was a pioneer 

 in developmental physiology. Interestingly 

 enough, he laid the foundation for the mass 

 of modern work on the summation of tem- 

 perature when (1735) he found that the 

 sum of the mean daily temperatures of air 

 in the shade made a constant for any given 

 phenological period. Abbe in a book com- 

 piled in 1891 and finally published in 1905 

 quotes a translation from Reaumur as fol- 

 lows: "It would be interesting to continue 

 such comparisons between temperature and 

 the epoch of ripening and to push the study 

 even further, comparing the sum of the 

 degrees of heat for one year with the 

 similar sums of temperature for many other 

 years; it would be interesting to make com- 

 parisons of the sums that are effective 

 during any given year in warm countries 

 with the effective sums in cold and tem- 

 perate climates, or to compare among 

 themselves the sums for the same months 

 in different countries." 



Reaumur expanded this statement else- 

 where into the suggestion that, since the 

 same grain is harvested in different cli- 

 mates, a comparison should be made of the 

 same temperatures for the months during 

 which the cereals accomplish the greater 

 part of their growth and maturity in warm 

 countries like Spain and Africa, in tem- 

 perate countries Hke France, and in cold 

 countries like those of the extreme north. 

 Here we have the background for the geo- 

 graphic application of temperature summa- 

 tion that underlies, in theory at least, 

 certain modern work such as the life zone 

 concept of Merriam and the "bioclimatic 

 law" of Hopkins. 



Gasparin in 1844, in commenting on 

 Reaumur's ideas on this subject, recognized 

 in them the germ of all work on the quan- 

 tity of heat necessary to mature different 

 kinds of plants. According to Abbe, Adan- 

 son, soon after Reaumur, disregarded sub- 

 freezing temperatures and took only the 

 sums of those above freezing. More than 

 three-quarters of a century later Boussin- 

 gault in 1837 in his Rural Economii com- 

 puted the total heat required to ripen grain 

 essentially according to Adanson's sugges- 

 tion. His data indicate that the required 

 number of dav degrees increases as the 

 latitude decreases. 



Quetelet (1846) added the idea of a 

 threshold of awakening from winter dor- 

 mancy; even so, in his summary (cf. Abbe, 



1905, p. 188) Quetelet used the sum of 

 temperatures, or the sum of the squares of 

 temperatures above freezing for his basic 

 data. Alphonse de CandoUe, by 1865, knew 

 that if the time in days required for seed 

 germination is multiphed by the accumulat- 

 ed degrees centigrade, the results are more 

 consistent if the minimum germinating tem- 

 perature for the species, rather than freez- 

 ing of water, is taken as the base. 



It remained to work out the physiological 

 zero for different plants. Gasparin (1844) 

 adopted 5° C. as the beginning of "effective 

 temperature." By 1852 (fide Abbe) he had 

 recognized that these early preoccupations 

 with temperature were faulty in that the 

 effect of other meteorological conditions 

 was also important in phenological affairs. 

 He suggested that rainfall, sunshine, and 

 related meteorological data should also be 

 considered in such analyses. 



Candolle (1865) found that, contrary 

 to the opinion of certain workers, some 

 seeds will germinate at 0° C. and possibly 

 at even lower temperature if the water can 

 be kept liquid. He knew about minimum, 

 maximum, and optimum germinating tem- 

 peratures and emphasized the difference 

 between effective and ineffective tempera- 

 tures. 



Abbe summarizes these and many other 

 records of the measurement of environmen- 

 tal factors and their effects on plants. 

 Among other matters, he reviews the modi- 

 fication of Boussingault's day degrees by 

 Tisserand (1875), who used hours of light 

 between sunrise and sunset multiplied by 

 the mean temperature to give "sunshine- 

 hour degrees." The data indicate that, 

 for the maturation of spring wheat and 

 barley, this mixed summation appears to 

 decrease as the latitude increases. 



Abbe also traces the development of in- 

 formation concerning the effect of light on 

 germination and growth of plants from 

 that of Edwards and Colin in 1834 through 

 the cautious conclusion of Pauchon (1880) 

 that light favors germination when the 

 seeds are below their optimum germinating 

 temperature. Abbe discusses the invention 

 by Arago before 1850 of thermometer cou- 

 ples composed of black-bulb and colorless 

 bulb pairs to measure total insolation, which 

 Marie-Davy improved. By 1867, Roscoe 

 knew from measurements in Europe and 

 Brazil that, unlike heat, the chemical action 

 of light reaches its maximum effect at noon 



