13« 



TRE AMERICAN NATURALIST [Vol. LI 



exist, but they are so extremely rare that one may admit 

 all cases of disputed origin and still have very little 

 asexual variation to accoimt for. 



I have never seen a published calculation of the fre- 

 quency of bud-variation, and presume it would be of little 

 value anyway, since the general evidence indicates a dif- 

 ferent frequency for different species and even for the 

 same species at different times. It may be mentioned, 

 however, that in personal examination of over 100,000 

 hills of potatoes belonging to several hundred varieties, 

 12 definite bud-variations have been seen, a frequency of 

 1 in 10,000; while just as careful a scrutiny of about 

 200,000 plants belonging to the genus Nicotiana has 

 brought to light but 1 case. 



Probably a more practical and just as satisfactory an 

 estimate of the frequency of bud-variations in economic 

 plants is the record of varieties that have been produced 

 in this manner. Naturally such a record contributes little 

 to theory because only a portion of the variations arising 

 are observed, and only a fraction of those observed are 

 propagated. Further, the origin of comparatively few 

 commercial varieties is known. Yet we may get some idea 

 of what to expect in the future, by noting what has oc- 

 curred in the past. 



Data gathered in this manner will appear to give us 

 different values depending on how we approach the 

 matter. For example, in Cramer's wonderful monograph 

 on bud- variation, the grape is cited as one of the species 

 that often varies in this manner. He cites some 25 or 

 more such varieties. Yet in the large list of American 

 grapes in Hedrick's ''Grapes of New York" only one 

 doubtful case of bud-origin is reported, 

 members that hundreds of varieties of grapes j 

 and millions of vines are examined each year, i 

 mont bv thi^ method mmmik ratli.-r hopelc-. And ex- 

 amination of tlio list of pi-.-..nt dav api.l<- 

 and cluMTi^-. of tlielui^li-fnilt-^. or nf putat, 



