220 Biology in America 



F. and relative humidity of 50-80% only the intermediate 

 form is obtained. Not only are these results given by dif- 

 ferent pairs of closely related individuals, brothers and sisters, 

 but the same pair when mated under different conditions give 

 different results. 



While Mendelian characters are evidently represented by 

 definite determiners in the germ cells, there is abundant evi- 

 dence that the development of these characters can be con- 

 trolled by environment. There is a sex-linked dominant 

 character in Drosophila known as abnormal abdomen, in which 

 the usual black bands upon the abdomen are irregular and 

 broken and may even be absent. That this character depends 

 on the type of food (whether wet or dry) for its development 

 may be shown by the following experiment. If an abnormal 

 male be crossed with a normal female and the larvae fed on 

 wet food, the daughters will be abnormal and the sons normal ; 

 but if the food be dry, both daughters and sons will be 

 normal. From these latter daughters however abnormal off- 

 spring may be obtained if the conditions are favorable, show- 

 ing that the determiner for abnormality is present, regardless 

 of external conditions, but the . development of the character 

 itself is dependent upon this latter factor. 



The influence of environment in determining the form of 

 the individual animal or plant is so well known as to be 

 commonplace. Food, temperature, pressure, moisture, chem- 

 icals, radiation may, one or more, so profoundly change the 

 development of an organism that two differently cultured 

 individuals may not be recognizable as members of the same 

 species. 



The effect of environment on individual development is 

 perhaps nowhere more strikingly shown than in many species 

 of mountain plants, which range from the low moist valleys- 

 to the high arid slopes above timber line. Seeds of the same 

 species will produce in the former situation tall stemmed 

 plants, with large thin leaves, small roots and pale flowers, 

 which require from two to three months to mature seecl ; while 

 in the latter environment they develop plants with short stems, 

 small, thick leaves, and bright colored flowers, which set seed 

 within a few weeks after the blossoms open; all of which, 

 possibly excepting the flower color, are adaptations to their 

 different environments. 



A test of the influence of the environment upon plants has 

 been made by the Department of Botanical Research of the 

 Carnegie Institution, by the introduction of various species 

 of plants into areas having very different climates, in the hot 

 dry desert at Tucson, Arizona, in the cool climate of the 

 neighboring mountains, and in the cool moist climate of the 



