8 The Plant Wori.d. 



In general, American breeders are committed to the prin- 

 ciple of the isolation of individual plants. Continental breeders, 

 with some notable exceptions, were evidently much slower in 

 utilizing this idea and it is doubtful if even now the value of the 

 method is fully appreciated. Thus it is likely that Johannsen's 

 paper is best appreciated by European breeders who have held 

 to the idea that selection within a variety has brought about a 

 rapid change or type-shifting, such change being really only an 

 isolation of types or fines that breed comparativjly true. Jo- 

 annsen made this idea emphatic, but at the time of the appear- 

 ance of his paper American breeders had largely developed away 

 from the idea that selection en masse brings about any shifting 

 of the type. 



While American breeders in endeavoring to obtain a pure 

 type of a self-pollinated form, do not select en masse, yet many 

 experiments that are being conducted are almost certainly being 

 vitiated in part by the failure to recognize the existence of 

 pure lines in breeding true within one variety. These lines 

 manifestly have diflferent yielding capacities, under the same or 

 different condition?. The whole question of acclimatization 

 needs to be reviewed, as far as the types of plants under consid- 

 eration are concerned. The experiments that have been made in 

 the changing of seed grain from one region to another may need to 

 be re-investigated. The continued selection of large and small 

 seed grain from an original population would doubtless be noth- 

 ing else than the more or less complete isolation of the various 

 types. In such experiments the material needs to be subjected 

 to a more critical biological analysis than has hitherto been ac- 

 corded. As Johannsen indicated, the principle of pure lines 

 may help in explaining "degeneration" which often appears to 

 take place in certain crops. 



As indicated, Johannsen endeavored to change the mean 

 within the pure lines by selecting extremes of seeds as parents. 

 A slight change was made in the relative breadth of seeds but 

 the cl r.r.gc may have been accidental. Johannsen's conclusion 

 ir, "tl-c f r-rsonal quality of the parents, grand parents or some 

 oti.cr rxccGtor has no influence, so far as my studies go, upon 

 t'-c avcrcrc character of the individual." Galton evidently con- 



