98 THE SURVIVAL OF THE UNLIKE. [ill. 



contemporaneous leaves, which records the connection 

 between the two, is sufficiently rare to escape comment. 

 Various writers have remarked upon the similarities of 

 these occasional leaves to geologic types, but, so far as I 

 recall, they regard them as remnants or vestiges of the 

 ancient types rather than as reversions to them. There 

 is this important difference between a remnant and a 

 reversion. A remnant or rudiment is more or less uni- 

 formly present under normal conditions, and it should 

 give evidence of being slowlj^on the decline; whilst a re- 

 version is a reappearance of wholly lost characters under 

 unusual or local conditions. Now, my chief reasons for 

 considering these sports to be reversions is the fact that 

 they occur upon the sterile and verdurous shoots, the very 

 shoots which are most likely to vary and to revert, be- 

 cause they receive the greatest amount of food supply, as 

 Darwin has shown to be the case with independent plants. 

 I am thus able, therefore, to make still another analogy 

 between phytons and plants, and to illustrate again the 

 essential sameness of bud -variations and seed -variations. 



III. 



I now wish to recall your attention more specificallj^ 

 to the subject of asexual or purely vegetative variation. 

 I have shown that no two branches are alike any more 

 than any two plants are. I have also cited the frequent 

 occurrence of differences so marked that they are called 

 bud -varieties or sports. Carriere enumerated over one 

 hundred and fifty of them of commercial importance in 

 France, and, as nearly ns 1 can estimate, there are no 

 fewer than three hundred named horticultural varieties 

 grown at the present moment in this country whi(!h had 



