l8o BOTANICAL GAZETTE [march 



Let US now consider the production of new forms analogous to 

 the mutations of O. Lamarckiana observed in alKed 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 con- 

 sidered 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 O. 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 O. biennis h. It had 

 evidently arisen there by mutation.™ From it a constant strain 

 has been derived, which is still in cultivation.^' Among about 

 600 plants of this variety a single dwarf arose in 1903.^'' It had 

 all the marks of O. 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, O. 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 in 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 O. Lamarckiana, and that, even if this latter 

 species should have to be considered as a hybrid, mutability can- 

 not be explained as a result of such a condition, since there is not 

 the least doubt concerning the gametic purity of 0. biennis L.^"* 



=» Die Mutationstheorie. Leipzig. 1900; see 2:599. 



" Pure seeds of this pure strain I shall be glad to send to any botanist interested 

 in these questions. 



" tjber die Dauer der Mutationsperiode bei Oenothera Latnarckiana. Ber. Deutscb. 

 Bot. Gesells. 33:387. 1905. 



=3 Stomps, Th. J., Mutation bei Oenothera biennis L. Biol. Centralbl. 32 :S32. 1912. 



^ Davis, B. M., Mutations in Oenothera biennis L. Amer. Nat. 47:116. 1913; 

 also Parallel mutations in Oenothera biennis L. Amer. Nat. 48:498-501. 1914. 



