_ TWIN HYBRIDS (LAETA AND VELUTINA) AND THEIR 
ANATOMICAL DISTINCTIONS 
FRANK M. ANDREWS 
* She Ft ent ae 
Twin hybrids are produced according to DEVRIEs “by the com- 
binations Oenothera biennis xO. Lamarckiana, and O. muricataXO. 
Lamarckiana, and by those of some of their derivatives.”! Besides 
laeta and velutina I shall describe here O. Lamarckiana and O. 
biennis. O. biennis, along with some other species, was introduced 
into Europe a long time ago. The origin of O. Lamarckiana, or 
large-flowered evening primrose, is involved in obscurity. In an old 
potato field near Hilversum, in the year 1886, DEVRreEs? found a 
great many specimens of O. Lamarckiana which were observed to be 
in a state of mutability. I have visited this primrose field to observe 
and collect specimens. There are comparatively few of them left, due 
to the fact that they are rapidly being crowded out by pine trees that 
have been planted there. It is apparently only a question of a little 
time, unless something intervenes, until they will have disappeared 
entirely from that locality. O. Lamarckiana produced new forms by 
mutation, not only in the wild state in the field near Hilversum, but 
also in cultivation. This latter fact was proved by transferring rosettes 
from the field to the garden, where the plants could be protected and 
watched throughout their entire existence. This method, together with 
that of sowing the seeds’ of these plants under controlled conditions, 
has allowed quite a number of mutants to assert themselves and to be 
recognized. Unless such methods as were introduced by DEVRIES 
in his garden at Amsterdam are followed, the detection of a mutation 
is much more apt to be only accidental. Furthermore, these methods 
___ when used for rapid multiplication in the garden under controlled and 
___ protected conditions may also be conducive to an increase of mutants, 
and hence their more certain and frequent recognition. For “sucha 
tapid multiplication in the course of a comparatively few years’ (as 
eg RS Ae ee a i ee na eae eae ed 
RAS FES A net A te ot nee eg) Bee ele 
* DeVries, Huco, On twin hybrids. Bot. GAZETTE 44:401-407. 1907. 
? DeVries, Huco, Mutationstheorie 1:152, 401-407. 
a 3 DeVries, Huco, Species and varieties, p. 525. 1905- 
193) [Botanical Gazette, vol. 50 
