IV. THE SUDDEN APPEARANCE AND THE 

 CONSTANCY OE NEW VARIETIES. 



§ 8. EXA]\IPLES OF CONSTANT RACES. 



Horticultural varieties are generally constant ; excep- 

 tions to this rule are usually noted expressly in the text- 

 books. Most varieties are not only constant from seed 

 but also pure. By constant is meant that in ordinary 

 cultivation they produce no more impurities than are un- 

 avoidable (that is to say, at most 3%). Absolute purity 

 means that when isolated under experimental conditions 

 the seeds reproduce their own variety without exception. 

 Constanc}' in this case is complete, but it is seldom of 

 practical interest to bring either the old established sorts 

 or the novelties to this pitch of purity, or even to find 

 out how closely they approach it. 



This has, however, been repeatedly done by scientific 

 investigators and especially by Darwin and Hoffmann.^ 

 Insufficient familiaritv with the dancfer of chance cross- 

 ings robbed the results of the older investigators of much 

 of their value as evidence, except of course in those cases 

 where the race proved constant. The large number of 

 observations of instances of complete constancy were ob- 



^ See the Riickhlick aiif mcinc CuJfurvcrsnchc of the latter author 

 in the Botanischc ZcituivJ, t88i, and tlie hterature cited there. Ihne 

 and ScHROTER have given a complete Hst of Hoffmann's papers in 

 the obituary of him in Bcrichtc d. d. hot. Gesellsch., Vol. X, 1892, p. 

 18 of the last part. 



