No. 603] 



BUD-VABIATION 



137 



may not be the direct cause of such a modification. Dr. 

 H. J. Webber once informed the writer that immediately 

 after the great Florida freeze of the early nineties bud- 

 variations in the citrus fruits of that region were greatly 

 increased. Such variations may have been induced by 

 the freezing, but they were not adaptive variations. 



The conclusions reached thus far have not involved a 

 point of theory which practically is difficult to separate 

 from the one just discussed. It is this. If we disregard 

 adaptive variations, is there not still a reason for select- 

 ing fluctuations? Are there not internal factors which 

 so act that there is a narrow but appreciable variability 

 in an asexually produced population which may offer a 

 basis for selection! In other words, how constant is an 

 asexually propagated race? 



We can make an effort to compute the frequency of 

 marked bud- variations. But have we any right to assume 

 that these represent the sum total of all bud- variations ? 

 Are not bud-variations and perhaps all inherited vari- 

 ations like residual errors, the small ones frequent, the 

 large ones rare? This may be the case, but I should like 

 to emphasize the fact that we have no true criterion for 

 determining the size of a variation. A variation that ap- 

 pears large by visual criteria may be an extremely small 

 change in the constitution of the plant, and vice versa. 

 In view of this fact together with the practical consid- 

 eration that commercially valuable variations must be 

 measurable within a reasonable duration of time— say a 

 lifetime— it is by no means certain that we are going far 

 astray in calculating the frequency of bud-variations by 

 the so-called marked jumps or mutations. 



Furthermore the range of the fluctuations of asexually 

 propagated varieties of most species is very small even 

 when broadened— as it always is— by the addition of the 

 effects of variable external conditions. It is not hard to 

 recognize a Winesap apple, a Clapp's Favorite pear or a 

 Concord grape, even though these varieties have been 

 grown extensively for a considerable number of years. 

 Certain local snbvarieties of the pome fruits are said to 



