272 NATURE SKETCHES IN TEMPERATE AMERICA 



study of nature being not only the development of the observa- 

 tional powers, but to arouse interest in the philosophy of life. 

 While a great deal is learned from observational study of nature 

 afield, there is a growing interest in experimental work supple- 

 menting field study. It is well known, for instance, that the 

 so-called seasonal dimorphism in butterflies — that is, difference 

 in color in the summer and winter broods — is mainly due to 

 the influence of temperature. By subjecting the pupje to high 

 or low temperature one or the other type of coloring can be 

 produced in the laboratory at will. Breeding experiments are 

 also of great importance in the study of evolution. 



The best of all experiments in evolution, says Clements,^ 

 "are those that are constantly being made in nature. Such 

 experiments are readily discovered and studied in the case of 

 origin by adaptation. Variants (which are new forms resulting 

 from variation) present greater diflSculties; while mutants 

 (which are sudden changes) are very rare under natural 

 conditions." 



It is well to note here that some forested tracts should be 

 set aside as natural preserves for the benefit of the general 

 nature-loving public. Some of the pleasures one may enjoy 

 by contact with nature are set forth in those sketches. Such 

 a forest as is jnctured on the opposite page - is both an in.spira- 

 tion and delight to the nature lover. Some of these tracts 

 of wild lands still abound, and should be ])reserved before it 

 is too late. The jiresent movement for tiie conservation of 

 these beautiful wooded areas is most timely and imperative. 

 Their preservation is due our future generations. This con- 

 servation should also include tracts of wild accessible land 

 not necessarily forested, having its natural fauna and flora 

 undisturbed, yet should contain diverse topographical features. 

 These parks should furnish the necessary grounds for that 

 growing population who desire to make field trips whether it 

 be for recreation, nature study, or the searching into the deeper 

 problems of biological science. 



' "Research Methods in Ecology." 

 ^ At Kenilworth, Illinois. 



