IV. THE SUDDEN APPEARANCE AND THE 
CONSTANCY OF NEW VARIETIES. 
8. EXAMPLES 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. 
Constancy 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 DAR\VIN and HOFFMANN. 1 
Insufficient familiarity with the danger 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- 
1 See the Riickblick auf meinc Culturvcrsuchc of the latter author 
in the Botanischc Zeitung, 1881, and the literature cited there. IHNE 
and SCHROTER have given a complete list of HOFFMANN'S papers in 
the obituary of him in Bcrichte d. d. bot. Gescllsch., Vol. X, 1892, p. 
18 of the last part. 
