EXTERNAL INFLUENCES AS CAUSES OF VARIATION 221 



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the type ; (2) by affording or withholding the opportunity for the 

 proper development of the characters born into the individual and 

 therefore representing internal forces ; (3) by exerting, directly 

 upon the organism, a stimulating or a depressing effect upon its 

 normal activities ; (4) in extreme cases by temporarily or per- 

 manently modifying the character of normal functions. 



The first manifestly affects the type and the race as a whole, 

 while the second, third, and fourth primarily affect the individual. 

 It is with these latter that we are now concerned. 



The hasty student credits to external conditions all that would 

 happen if these conditions were withdrawn. This is erroneous. 

 A very large part of all that happens is due primarily to internal 

 causes, because different races are differently affected by the same 

 conditions. The fundamental cause of variability is therefore to 

 be sought in the form of inherited characters, even though these 

 are dependent upon external conditions for their development, 

 which may themselves seem to be direct causes of variation. 



It is therefore proper enough to speak of external conditions 

 of life as causes of variability, providing we know what we mean 

 thereby and are careful to distinguish between their indirect 

 effect, on the one hand, in affording or withholding the con- 

 ditions of development in which their influence is secondary, 

 and their direct influence, on the other hand, in stimulating, 

 depressing, or altering the activities of the organism. 



With these distinctions in mind we may study the effects of 

 outside conditions upon variability without danger of attributing 

 to them what properly belongs to inherited faculties. 



SECTION I GENERAL EFFECT OF LOCALITY UPON PLANT 

 AND ANIMAL DEVELOPMENT 



It is a matter of common knowledge that the texture and 

 quality of garden vegetables depend very much upon the con- 

 ditions under which they are grown, and that the highest flavor 

 of the orange, peach, pineapple, and edible fruits generally is 

 found only in specimens from certain favored localities. 



Thus cantaloupes of extremely high quality developed first at 

 Rockyford, Colorado, and afterward in a few other sections. 



