20 



THE fflSTORY OF ECOLOGY 



tended drying were known. For example, 

 Cooke (1895) summarized instances that 

 show the tenacity of life of desert snails. 

 One of the most spectacular concerns two 

 specimens of Helix desertorum that were 

 glued to appropriate supports and exhibited 

 in the British Museum from March 26, 

 1846, to about March 15, 1850, when one 

 revived and fed after being placed in water. 



Bachmetjew (1907) cites a fairly rich 

 literature which grew during the latter 

 half of the nineteenth century dealing with 

 the eflFect of humidity upon the develop- 

 ment of insects and insect populations and 

 upon such other matters as body form and 

 color. 



By 1890 many of the essential relations 

 of osmosis had been worked out for plant 

 cells by PfeflFer (1877) and De Vries 

 (1884). It had been known for an even 

 longer time that the ameba shrinks in a 

 weak saline solution and swells on return 

 to fresh water (Kiihne, 1864). In the late 

 1870's Schmankewitsch reported that if the 

 fresh-water flagellate Anisonema acinus is 

 cultivated for many generations in water to 

 which sea salt is added gradually, its struc- 

 ture is modified, and Griiber (1889) 

 changed the marine form of the heliozoan 

 Actinophrys sol to the more vacuolated 

 fresh-water form, and vice versa. 



Davenport (1897) could make the gen- 

 eralization that the capacity for resistance 

 to stronger salt solutions seems to be closely 

 correlated with the conditions of the medi- 

 um in which the organism has been reared; 

 he cited a series of observations dating 

 back to those of Beudant (1816) and show- 

 ing that mollusks living in the diluted sea 

 water of littoral regions, such as Ostrea or 

 Mytiliis, could resist the ill eflFects of expo- 

 sure to fresh water better than mollusks 

 from the open sea. Beudant also showed 

 experimentally that fresh-water and marine 

 organisms could go far towards becoming 

 accustomed gradually to the opposite type 

 of medium, or, in more general language, 

 that by varying the density of the culture 

 medium slowly, we may, with time, vary 

 the resistance of individuals. Such experi- 

 ments were much extended during the 

 nineteenth century as, for example, by Pla- 

 teau (1871) on the fresh- water isopod 

 Asellus and bv others on representatives 

 of almost all the principal animal groups. 

 Schmankewitsch's oft-quoted experiments 

 (1875) in which he transformed the brine 



shrimp Artemia salina to the so-called A. 

 milhaiiseni and back by rearing it in differ- 

 ent concentrations of salt water are prob- 

 ably the most dramatic of these otherwise 

 half- forgotten experiments. A consideration 

 of the relation of mineral nutrients, espe- 

 cially those of the soil, to the growth of 

 plants led to the strong emphasis that 

 Liebig (1840) placed on what is now 

 known as Liebig's "law of the minimum" 

 (seep. 198). 



Experimental analysis of the effect of 

 hght extended throughout this period. Ed- 

 wards (1824) stated that tadpoles would 

 not develop well in the dark. Others in the 

 fifties and sixties found no effect of light 

 or darkness on the rate of growth, while 

 Yung (1878) claimed that tadpoles grew 

 more rapidly in length in the light. Wood 

 (1867) reported a positive influence of re- 

 flected light on the color of butterfly 

 chrysalids. 



Modem work on the effect of wavelength 

 of light on animal development apparently 

 began with that of Beclard (1858), and the 

 foundation for present knowledge concern- 

 ing the relation between wavelength and 

 photosynthesis was laid by Draper (1844), 

 Sachs (1864), and Pfeffer (1871). For 

 plants that contain chlorophyll, it became 

 known that, within limits, the rate of assim- 

 ilation decreases as light intensity decreases 

 (Reinke, 1883, 1884). For plants and other 

 organisms, the most diverse upper limits of 

 intensity were known by 1896. Experimen- 

 tation on the lethal effect of light on bac- 

 teria dates back to Montegazza, according 

 to Nickles (1865), and was first studied 

 with thoroughness by Downes and Blunt 

 (1877, 1878), who found that the blue end 

 of the spectrum was actively bactericidal, 

 but that red was not similarly effective. 



Organisms are normally subjected to a 

 diurnal period of darkness and of light. 

 Smith (1933) says that the first mention 

 in literature of the influence of the length 

 of day on plants is found in the writings 

 of Linnaeus, in 1739. Linnaeus thought, 

 however, that the rapid growth and speedv 

 maturity of arctic plants result from heat 

 rather than from the light supplied by the 

 lengthened davs. Davenport (1897, p. 421) 

 records that Trew in 1727 had studied 

 the effect of alternation of light and dark- 

 ness on the rate of growth in plants. Once 

 opened, the subject attracted attention, but 

 it was not until the work of Sachs (1872) 

 that a continuous curve of plant growth 



