204 SELECTION. Chap. XX. 



usually accompanied by modifications in the other, though 

 not necessarily to the same degree. With the plum-tree, 

 for instance, some varieties produce plums which are nearly 

 alike, but include stones extremely dissimilar in shape; 

 whilst conversely other varieties produce dissimilar fruit 

 with barely distinguishable stones ; and generally the stones, 

 though they have never been subjected to selection, differ 

 greatly in the several varieties of the plum. In other 

 cases organs which are not manifestly related, through 

 some unknown bond vary together, and are consequently 

 liable, without any intention on man's part, to be simul- 

 taneously acted on by selection. Thus the varieties of the 

 stock (Matthiola) have been selected solely for the beauty of 

 their flowers, but the seeds differ greatly in colour and some- 

 what in size. Varieties of the lettuce have been selected solely 

 on account of their leaves, yet produce seeds which likewise 

 differ in colour. Generally, through the law of correlation, 

 when a variety differs greatly from its fellow- varieties in any 

 one character, it differs to a certain extent in several other 

 characters. I observed this fact when I cultivated together 

 many varieties of the same species, for I used first to make a list 

 of the varieties which differed most from each other in their 

 foliage and manner of growth, afterwards of those that differed 

 most in their flowers, then in their seed-capsules, and lastly 

 in their mature seed ; and I found that the same names gene- 

 rally occurred in two, three, or four of the successive lists. 

 Nevertheless the greatest amount of difference between the 

 varieties was always exhibited, as far as I could judge, by 

 that part or organ for which the plant was cultivated. 



When we bear in mind that each plant was at first culti- 

 vated because useful to man, and that its variation was a 

 subsequent, often a long subsequent, event, we cannot explain 

 the greater amount of diversity in the valuable parts by 

 siij^posing that species endowed with an especial tendency to 

 vary in any particular manner were originally chosen. We 

 must attribute the result to the variations in these parts 

 having been successively preserved, and thus continually 

 augmented; whilst other variations, excepting such as in- 

 evitably appeared through correlation, were neglected and 



