THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 11 



It is obvious that the fact that mutations may be artificially 

 induced in hybrid strains does not contradict the contention that 

 they may arise in pure strains also. But from the experiments of 

 Tower it seems that some hybrid strains at least are more liable 

 to show the phenomenon. 



Let us now consider the production of new forms analogous to 

 the mutations of 0. Lamarckiana observed in allied species. The 

 theoretical significance of these facts lies in the proof that any 

 hypothesis to explain such phenomena on the ground of qualities 

 which are special to Lamarck's evening primrose is to be considered 

 as wholly inadequate. 



The first instance of mutability shown by another species than 

 0. Lamarckiana was the production of a dwarf by 0. biennis 

 cruciata, a form which is now to be described as 0. biennis var. 

 leptomeres Bartl. This form was first discovered in 1900 by my 

 son Ernst de Vries in the sand dunes near Santpoort in Holland, 

 where a single specimen of 0. biennis bore linear petals, while all 

 the surrounding individuals were normal 0. biennis L. It had 

 evidently arisen there by mutation. 1 ) From it a constant strain 

 has been derived, which is still in cultivation. 2 ) Among about 

 600 plants of this variety a single dwarf arose in 1903. 3 ) It had 

 all the marks of 0. biennis L. combined with the stature of a dwarf 

 and the linear petals of the parent form. 



Shortly afterward Stomps discovered, in his cultures of hybrids 

 between this cruciata variety and the original species, another 

 dwarf and, moreover, a new mutant type, 0. biennis semigigas.*) 

 Both arose from guarded seeds without any intermediate steps, 

 in the same way that the mutants of 0. Lamarckiana are known 

 to arise. They had cordate petals, the dwarf having on other respects 

 the same characters as the dwarf of 0. biennis leptomeres, and the 

 semigigas having 21 chromosomes in its nuclei. Stomps was the 

 first to lay stress on these facts as a proof that mutability is not 

 limited to 0. Lamarckiana, and that, even if this latter species 

 should have to be considered as a hybrid, mutability cannot be 



i) Die Mutationstheorie, Leipzig, 1900; see 2:599. 



2) Pure seeds of this pure strain I shall be glad to send to any 

 botanist interested in these questions. 



3) Ueber die Dauer der Mutationsperiode bei Oenothera Lamarckiana. 

 Opera VI, p. 374. 



4) Stomps, Th. J., Mutation bei Oenothera biennis L. Biol. Centralbl. 

 32:532, 1912. 



