ON BIASTREPSIS IN ITS RELATION TO CULTIVATION. 155 



isolated individuals of Dipsacus sylvestris with twisted stems a 

 breed can be produced by selection, such that the abnormality 

 recurs annually in a larger or smaller number of the plants raised 

 from seed. 



Such hereditary breeds or races afford the best material for com- 

 parative investigation of the conditions upon which the develop- 

 ment of abnormalities depends. According to circumstances each 

 successive generation is richer or poorer in so-called 'heirs'; that is, 

 in individuals which manifest the monstrosity. If the breed is in 

 itself poor in heirs, that is, if it shows, even after careful annual 

 selection of the seed-producers, only a small percentage of mon- 

 strous individuals, it is one which is obviously not suitable as material 

 for such an investigation; but if, on the contrary, under normal 

 conditions, 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 purpose 

 to describe in this paper and which were almost exclusively 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 investigation. 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, fasciations, 

 etc., 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 variations; 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 



