ECOLOGICAL BACKGROUND AND GROWTH BEFORE 1900 



21 



was obtained, demonstrating clearly that 

 growth increases during tlie night, has a 

 maximum about daybreak, and then falls to 

 a minimum about sunset. Garner (1936) 

 traced the development of photoperiodicity. 

 Moleschott (1855) reported that the frog, 

 Rana escidenta, produces carbon dioxide 

 more rapidly in light than in darkness; and 

 Bidder and Schmidt (1852) had found that 

 starving cats show a diurnal rhythmicity in 

 loss of weight, with least rapid loss during 

 the night. It would be interesting to know 

 if temperature changes were properly 

 controlled. 



Schiifer (1907) was the first person in 

 the present century to present evidence that 

 length of day is a factor in bird migration. 

 He traces the idea back to a Swedish poet, 

 Runeberg, who was reported in 1874 to 

 have thought that "it is the longing after 

 hght, and that alone, that diaws the birds 

 southward" in the autumn, and that they re- 

 turn to the long days of the Scandinavian 

 summer for the same reason. The views of 

 Runeberg did not pass unchallenged, for 

 Newton (1874) objected that since both 

 autumn and spring migrations are initiated 

 before the respective equinoxes, the birds 

 in both instances are journeying toward 

 increasingly shortened days. 



Apparently without knowing about Rune- 

 berg's ideas, Seebohm (1888) wrote con- 

 cerning the autumnal migration: "The an- 

 cestors of the Charadriidae were probably 

 not in search of warmth for the climate of 

 the Polar Basin was in those remote ages 

 mild enough: nor in search of jood, which 

 was probably abundant all the year round; 

 but in search of light during the two or 

 three months when the sun never rose 

 above the horizon." Schiifer comments on 

 the fact that Seebohm apparently did not 

 realize that birds might return to the arctic 

 region on account of the lengthened days 

 to be found there. 



The custom of providing domestic fowls 

 with added Hght in order to increase egg 

 production is said to be traceable to Spain 

 in 1802. The practice was introduced into 

 North America in 1895. The effects of the 

 increased length of the light period on the 

 egg production of hens becomes evident 

 in ten to twelve days' exposure. The same 

 practice is now applied in the raising of 

 fowls for food. 



Many observers, from Spallanzani (1787) 

 and Saussure (1796) down to Brues 

 (1939), have been interested in collecting 



data on animals and plants of thermal 

 waters. 



Dutrochet (1837), for plants, and Klihne 

 (1859), for animals, head a long fine ol 

 distinguished workers who agree that, with- 

 in hmits, an increase of heat accelerates 

 protoplasmic movement. Semper (1881, p. 

 129) could cite sound data to show that 

 an increase in temperature strikingly in- 

 creases the rate of development of many 

 animals and concluded, accurately enough: 

 "Many other examples might be added . . . 

 all providing the same effect of a rising 

 temperature; but, unfortunately, so far as 1 

 know, none give an exactly determined 

 tlrermal curve for particular species . . ." 

 The first such curve to be pubHshed ap 

 pears to have been that by Lilhe and 

 Knowlton (1897). 



Modern interest in the degree of heat re- 

 quired to produce death dates to Spallan- 

 zani (1787). Edwards (1824), Dutrochet 

 (1837), and Bert (1876) are among those 

 who investigated it. Unfortunately, experi- 

 mental conditions were not carefully con- 

 trolled and standardized. Even so, the work 

 of this period fairly well fixed the ideas that 

 prevail today and supplies much of our 

 present information on this subject. In gen- 

 eral, this early work showed that while 

 certain flagellates were not killed, under 

 the conditions used, until about 50° C, and 

 while for many groups 45° C, or there- 

 abouts, represents a common death point, 

 the majority of the metazoa are killed below 

 40° C. or even below 35° C. 



Temporary cold rigor and death point as 

 a result of low temperature similarly at- 

 tracted attention, particularly from 1860 to 

 1890. The information was sufiBcient to al- 

 low Davenport (1897) to make the sound 

 generalization that there is no fatal minimal 

 temperature for desiccated protoplasm. At 

 the other extreme, according to Doyere 

 (1842, p. 29), rotifers and tardigrades, 

 which in water are killed before the tem- 

 peratmre reaches 50° C, after drying may 

 be heated to 120° C. and still survive. This 

 supplies further evidence of the increased 

 resistance of dried protoplasm. Semper 

 (1881, p. Ill) cited as a recent discovery 

 that hibernating mammals have a consider- 

 ably lowered temperature, which Horvath 

 had found to reach 2° C. in the ground 

 squirrel, CiteUus citeUus. 



Experiments on acclimatization to high 

 temperatures were also carried on in the 

 later decades of the nineteenth century. 



