The giant evening-primrose, though not taller in stature than _O. lamarckiana_, deserves its name because it is so much stouter in all respects. [534] 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 the 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. The _rubrinervis_ is in many respects a counterpart to the _gigasv, but its stature is more slender. The spikes and flowers are those of the _lamarckianav, but the bracts are narrower. Red veins and red streaks on the fruits afford a striking differentiating mark, though they are not absolutely lacking in the parent-species. A red hue may be seen on the calyx, and even the yellow color of the petals is somewhat deepened in the same way. Young plants are often marked by the pale red tinge of the mid-veins, but in adult rosettes, or from lack of sunshine, this hue is often very faint. [535] The leaves are narrow, and a curious feature of this species is the great brittleness of the leaves and stems, especially in annual individuals, especially in those that make their stem and flowers in the first year. High turgidity and weak development of the mechanical and supporting tissues are the anatomical cause of this deficiency, the bast-fibers showing thinner walls than those of the parent-type under the microscope. Young stems of _rubrinervis_ may be broken off by a sharp stroke, and show a smooth rupture across all the tissues, while those of _lamarckiana_ are very tough and strong.