1915] DE VRIES—OENOTHERA BIENNIS 183 
Lastly, mutations have been observed by H. H. Barrietr® 
to arise in O. stenomeres, a new species of Montgomery, Maryland. 
In the fourth generation of a pure strain, embracing 106 indi- 
viduals, he found three aberrant types. One was a self-sterile 
plant, the second had thick buds and short thick fruits, and the 
third was a stout and very hairy individual with densely hairy 
petals, which justify its new name O. stenomeres mut. lasiopetala. 
Hairy petals constitute quite a new discontinuous variation among 
the evening primroses, since all individuals of O. stenomeres, as 
well as the allied species now being studied in this respect, have 
petals which are glabrous, except under microscopic examination. 
From this list we see that at least seven species, besides 
O. Lamarckiana, are now known to be in a condition of mutability, 
namely O. biennis L., O. biennis Chicago, O. muricata L., O. atro- 
virens Bartl., O. suaveolens Desf., O. grandiflora Ait.,4 and O. 
stenomeres Bartl. Probably more or less numerous allied forms 
will prove to be in the same condition as soon as they are tried 
on a sufficiently large scale. Therefore, this mutability can no 
longer be explained on the ground of observed or supposed char- 
acters of O. Lamarckiana which would distinguish this species 
from the other types of the group Onagra. 
O. biennis L., the European type of the species, which is growing 
wild and in large quantities in the sand dunes of Holland, where 
it had already been observed and collected by LINNAEUS, is, next 
to O. Lamarckiana, the most suitable for researches concerning 
mutability. Davis says, ‘‘No wild species of evening primrose 
has been so long under experimental and field observation or is 
better known to the workers with Oenotheras than this plant. 
The species has proven uniform to a remarkable degree, and it 
would be difficult to find a type of Oenothera so free from suspicion 
of gametic purity. The species appears to have been in Hollan 
since pre-Linnean days, and is therefore very old. As material 
3 Bartiett, H. H., An account of the cruciate-flowered Oenotheras of the subgenus 
Onagra. Amer. Jour. Bot. 1:226-243. pls. 19-21. 1914; see p. 2 
3# Concerning the specific difference of the two last named’ ae which have often 
been considered as synonyms, see L’Oenothera grandiflora de Vherbier de Lamarck 
epee de biologie végétale ‘dédits a Gaston Bonnter, Rev. Gén. Bot. 25?:151-166. 
§. I. 1914 
