398 De Vries. — On Biastrepsis in its 
say one-third of the progeny show the variation, whilst the 
remainder are atavistic, it may be anticipated that changes in 
the external conditions will manifest their influence by causing 
fluctuations in this percentage. 
On this principle are based the investigations which I pur- 
pose to describe in this paper, and which were almost exclu- 
sively carried out with my twisted breed of Dipsacus sylvestris , 
after this had attained in the fourth generation a degree of 
heredity exceeding 30 per cent. 
The publication of the results which I have obtained during 
the last six or eight years has, furthermore, a practical object. 
I am convinced that the cultivation of this twisted breed, if 
generally adopted, would afford an easy means of investiga- 
tion. Since I showed that monstrosities in plants are, as 
a rule, hereditary, and more particularly that twisted forms 
can be cultivated in Botanic Gardens as hereditary breeds, 
investigations have, as a matter of fact, been made in various 
places. But it has become apparent that the cultivation of 
such breeds is not so simple a matter as it appeared to be at 
first. Whilst some botanists have succeeded in raising from 
seeds obtained from me as striking and as numerous monstrous 
specimens as I myself, others have been less successful. 
The cultivation of plants having twisted branches, fascia- 
tions, &c., makes greater demands on the gardener than that 
of normal plants of the same species. These monstrosities 
are, in the first place, only partial and not individual varia- 
tions ; certain parts only of the body deviate from the type 
in the given direction. Some parts only show the abnormality, 
and in the case of twisting (biastrepsis) it has so far been 
observed to extend over a larger or smaller area of the main 
stem or of the branches. 
Individual variations are obtained pure from pure seed ; 
the conditions of germination and of subsequent cultivation 
have no effect upon this. Hence their cultivation does not 
involve anything more than that of the species to which they 
belong. However, it often happens that the seed, obtained 
by exchange or by purchase, is not quite pure, and therefore 
