2 grains; that is, in the ratio of
100 to 43. The female form, therefore, is very much more fertile than the
hermaphrodite, as in the two last cases; but the hermaphrodite was necessarily
self-fertilised, and this probably diminished its fertility.
We may now consider the probable means by which so many of the Labiatae have
been separated into two forms, and the advantages thus gained. H. Muller
supposes that originally some individuals varied so as to produce more
conspicuous flowers; and that insects habitually visited these first, and then
dusted with their pollen visited and fertilised the less conspicuous flowers.
(7/17. 'Die Befruchtung der Blumen' pages 319, 326.) The production of pollen by
the latter plants would thus be rendered superfluous, and it would be
advantageous to the species that their stamens should abort, so as to save
useless expenditure. They would thus be converted into females. But another view
may be suggested: as the production of a large supply of seeds evidently is of
high importance to many plants, and as we have seen in the three foregoing cases
that the females produce many more seeds than the hermaphrodites, increased
fertility seems to me the more probable cause of the formation and separation of
the two forms. From the data above given it follows that ten plants of Thymus
serpyllum, if half consisted of hermaphrodites and half of females, would yield
seeds compared with ten hermaphrodite plants in the ratio of 100 to 72.
Pages:
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406