Although the perfect flowers of Leersia sometimes yield seeds, yet this
occurs so rarely, as far as hitherto observed, that it practically forms a
second exception to the rule.
As cleistogamic flowers are invariably fertilised, and as they are produced in
large numbers, they yield altogether a much larger supply of seeds than do the
perfect flowers on the same plant. But the latter flowers will occasionally be
cross-fertilised, and their offspring will thus be invigorated, as we may infer
from a wide-spread analogy. But of such invigoration I have only a small amount
of direct evidence: two crossed seedlings of Ononis minutissima were put into
competition with two seedlings raised from cleistogamic flowers; they were at
first all of equal height; the crossed were then slightly beaten; but on the
following year they showed the usual superiority of their class, and were to the
self-fertilised plants of cleistogamic origin as 100 to 88 in mean height. With
Vandellia twenty crossed plants exceeded in height twenty plants raised from
cleistogamic seeds only by a little, namely, in the ratio of 100 to 94.
It is a natural inquiry how so many plants belonging to various very distinct
families first came to have the development of their flowers arrested, so as
ultimately to become cleistogamic. That a passage from the one state to the
other is far from difficult is shown by the many recorded cases of gradations
between the two states on the same plant, in Viola, Oxalis, Biophytum,
Campanula, etc.
Pages:
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455