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 lamarckiana 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 lamarckiana. The fruits attain only half the normal 

 size, but are broader and contain fewer, but larger seeds. 



