THE MUTATION THEORY 353 
of the leaves. They are broader and shorter, and especially at the 
base they are broadened in such a way as to become apparently 
sessile. The stalk is very brittle, and any rough treatment may cause 
the leaves to break off. The young seedlings are recognizable by the 
shape of the first two or three leaves, and when more of them are 
produced, the rosettes become dense and strikingly different from 
others. Later leaves are more nearly like the parent-type, but the 
petioles remain short. The bases of the blades are frequently almost 
cordate, the laminae themselves varying from oblong-ovate to ovate 
in outline. 
The stems are often quite unbranched, or branched only at the 
base of the spike. Strong secondary stems are a striking attribute of 
the lamarckiana parent, but they are lacking, or almost so in the 
dwarfs. The stem is straight and short, and this, combined with the 
large crown of bright flowers, makes the dwarfs eminently suitable 
for bed or border plants. Unfortunately they are very sensitive, 
especially to wet weather. 
Oenothera gigas and O. rubrinervis, or the giant, and the red-veined 
evening primroses, are the names given to two robust and stout 
species, which seem to be equal in vigor to the parent-plant, while 
diverging from it in striking characters. Both are true elementary 
species, differentiated from /amarckianca in nearly all their organs and 
qualities, but not showing any preponderating character of a retrograde 
nature. Their differences may be compared with those of the elemen- 
tary species of other genera, as for instance, of Draba, or of violets, 
as will be seen by their description. 
The giant evening-primrose, though not taller in stature than 
O. lamarckiana, deserves its name because it is so much stouter in all 
respects. The stems are robust, often with twice the diameter of 
lamarckiana throughout. The internodes are shorter, and the leaves 
more numerous, covering the stems with a denser foliage. This 
shortness of internodes extends itself to the spike, and for this reason 
the flowers and fruits grow closer together than on the parent-plant. 
Hence the crown of bright flowers, opening each evening, is more dense 
and more strikingly brilliant, so much the more so as the individual 
flowers are markedly larger than those of the parents. In connection 
with these characters, the flower-buds are seen to be much stouter 
than those of Jamarckiana. The fruits attain only half the normal 
size, but are broader and contain fewer, but larger seeds. 
