VARIATION IN GENERAL 21 



breeder has spent his life and his substance in the vain attempt to 

 produce a desired intermediate between two forms, either one of 

 which are easily secured. The question arises, therefore, Are some 

 intermediates impossible ? Can we bridge the space between the 

 nectarine and the peach ? between the apricot and the plum ? 



With all these examples before us, we see at once that to pro- 

 ceed upon the theory of continuity is a gratuitous assumption 

 not borne out by facts. Force and physical agents generally seem 

 to be continuous in their different manifestations, shading one 

 into another with imperceptible gradations ; but organized matter, 

 living or non-living, seems to be constructed upon the plan of dis- 

 continuity, in which case we may expect to find differences that 

 are easily perceptible, and should not be surprised at the appear- 

 ance of wide spaces between nearly related forms or at these 

 remarkably distinct gaps that often occur between a standard 

 form and its offset, which Darwin called a " sport " and which we 

 in these days call a " mutant." 



With this view of the case, we should not expect to find all 

 nature united by imperceptible gradations, even providing all living 

 beings past and present could be assembled and assorted according 

 to nearest resemblances. Realizing the discontinuous nature of 

 all chemical combinations, living or non-living, we should expect to 

 find notable gaps representing spaces not taken by any possible 

 form, and appearing quite independent of any selective process. 



This distinction is exceedingly important at the outset of this 

 study. If all variations are continuous, then all shades of differ- 

 ence, however minute, may be expected to occur naturally, and 

 we may hope to secure them by breeding. If, however, some 

 variations are discontinuous, then for these characters minute 

 gradation is impossible, and we may expect descent to follow along 

 certain lines only. 



Most of the conditions of life are without doubt naturally con- 

 tinuous in their variations. This is certainly true of temperature, 

 moisture, light, and food. Discontinuity must therefore arise from 

 within, and is evidently connected with the nature of organisms. 

 This is not difficult to appreciate when we recall the essential 

 discontinuity of all chemical compounds or other organizations 

 built upon the basis of distinct units. 



