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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.
But perhaps the circumstances may change, or the whole strain may be dispersed and spread to new localities with different conditions. Some of the latter might be found to be favorable to the robust gigas, or to rubrinervis, which requires a drier air, with rainfall in the springtime and sunshine during the summer.
Or is it perhaps concealed among the throng, being distinguished by no peculiar character? If our gigas and rubrinervis were growing in equal numbers with the lamarckiana in the native field, would it be possible to decide which of them was the progenitor of the others?
Rubrinervis is a mutation from Lamarckiana, chiefly distinguished by red midribs in the leaves and red stripes on the sepals. When propagated from self-fertilised seed it produced about 95 per cent. of offspring with the same characters, and the remaining 5 per cent. mutants, one of which was laevifolia which had been found by De Vries among plants growing wild at Hilversum.
But besides these a rubrinervis made its appearance and flowered the following year. This fact at once revealed the possibility that the instability of lamarckiana might not be restricted to the three new types now under observation. Hence the question arose how it would be possible to obtain other types or to find them if they were present.
They obey the same general laws, become active under similar conditions, some of them being more easily awakened than others. The germs of the oblonga, lata and nanella are especially irritable, and are ready to spring into activity at the least summons, while those of gigas, rubrinervis and scintillans are far more difficult to arouse.
The unevenness of the surface of the leaves may increase as in lata, or decrease as in laevifolia. The tendency to become annual prevails in rubrinervis, but gigas tends to become biennial. Some are rich in pollen, while scintillans is poor. Some have large seeds, others small. Lata has become pistillate, while brevistylis has nearly lost the faculty to produce seeds.
The leaves of O. gigas are broader, of a deeper green, the blade more sharply set off against the stalk, all the rosettes becoming stout and crowded with leaves. Those of O. rubrinervis 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.
Albida, nanella and rubrinervis appeared in large numbers, and even scintillans, of which I had but a single plant in the previous generation, was repeated sixfold. New forms did not arise, and the capacity of my strain seemed exhausted.
Now when lata is produced it is believed that in the heterotypic division one pair passes into one daughter-cell instead of one chromosome of the pair into each daughter-cell, the other pairs segregating in the usual way. We thus have one daughter-cell with 8 chromosomes and the other with 6. This 6+8 distribution has actually been observed in the pollen mother-cell in rubrinervis.
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