THE MUTATION THEORY 483 



The rubrinervis is in many respects a counterpart to the gigas, btlt 

 its stature is more slender. The spikes and flowers are those of the 

 laniarckiana, 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. 



The leaves are narrow, and a curious feature of this species is the 

 great brittleness of the leaves and stems, especially on annual indi- 

 viduals, for example, on those that make their stem and flowers in 

 the first year. High turgidity and weak development of the mechani- 

 cal and supporting tissues are the anatomical cause of this deficiency, 

 the bast-fibres 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 laniarckiana are very tough and strong. 



Both the giant and the red-veined species are easily recognized in 

 the rosette-stage. The very young seedlings of the latter are not 

 clearly differentiated from the lamarckiana, and often a dozen leaves 

 are required before the difference may be seen. Under ordinary 

 circumstances the young plants must reach an age of about two 

 months before it is possible to discern their characters, or at least 

 before these characters have become reliable enough to enable us to 

 judge of each individual without doubt. But the divergencies rapidly 

 become greater. The leaves of 0. gigas are broader, of a deeper 

 green, the blade more sharply set off against the stalk, the whole 

 rosettes becoming stout and crowded with leaves. Those of 0. rubri- 

 nervis on the contrary are thin, of a paler green and with a silvery white 

 surface; the blades are elliptic, often being only 2 cm. or less in width. 

 They are acute at the apex and gradually narrowed into the petiole. 



It is quite evident that such pale narrow leaves must produce 

 smaller quantities of organic food than the darker green and broad 

 organs of the gigas. Perhaps this fact is accountable partly, at least, 

 for the more robust growth of the giant in the second year. Perhaps 

 also some relation exists between this difference in chemical activity 

 and the tendency to become annual or biennial. The gigas, as a rule, 

 produces far more, and the rubrinervis far less biennial plants, than 

 'lie lamarckiana. Annual culture for the one is as unreliable as 



