SELF-FERTILIZATION OF PLANTS. 333 
above, noted a corresponding fact of plants being self-sterile in the spring or early in 
the summer. Müller remarks the following curious fact about Cardamine pratensis 
(* Befruchtung, Ee p. 134) :— 
“In fine weather the anthers of the tallest stamens twist outwards on dehiscing, and are thus 
favourably situated for the removal of the pollen by insects. In cold and rainy weather, however, one 
often finds flowers in which the twist is much slighter, or does not exist at all; consequently the 
pollen of the taller stamens then falls on the stigma.” 
He, moreover, adds that, in most flowers, one finds both the shorter stamens below 
the. stigma; but in some they are rather longer, and in others of the same height as 
the stigma. In these latter flowers, therefore, even the shorter stamens secure self- 
fertilization. Scrophularia nodosa, Müller observes, sets seeds abundantly in cold 
weather and in the absence of wasps. 
Mr. Darwin, in an article on ** The Sterility of Plants from changed Conditions of Life 
and from other Causes " (Anim. and Pl. under Domest. ii. p. 163), says that ** Linnzus 
long ago observed that Alpine plants, although naturally loaded with seed, produced 
either few or none when cultivated in gardens." There are, however, exceptions. One 
cause may be suggested besides the absence of necessary insects, namely, that the 
warmer temperature of the garden may have brought about sterility, as was the ease 
with Eschscholtzia. 
4.ix. Grafting. This appears to be a means by which self-fertilization may be reco- 
vered; for Mr. Darwin records the fact that Passiflora alata, from being naturally self- 
sterile, became self-fertile when grafted upon another species (Anim. & Pl. under 
Domest. ii. p. 164). 
4*. On the origin of conspicuous flowers, and. the causes which induce reversion to self- 
fertilization. Having enumerated the different ways by which self-fertility is regained, it 
will be advisable to explain here what I believe to be the immediate causes ofits recovery. 
In speaking of the “immediate cause ” of self-sterility, Mr. Darwin attributes it in 
most cases to * the conditions" to which the plants have been subjected. These should, 
I believe, be rather called the “ proximate causes,” the immediate being, as it seems to 
me, the undue preponderating influence of the exterior whorls of the flower—that is to 
say, the stamens and corolla especially, and, in addition to them, the glandular secreting 
organs. These, by being greatly stimulated by the repeated visits of insects, tend to 
become hypertrophied.’ Hence the corolla enlarges, becomes more brightly coloured, 
the nectariferous organs increase the quantity of secretion, and the stamens develope 
more pollen. Such being the case, nourishment is withheld from the pistil, which is 
delayed in its development; consequently such a flower is very generally proterandrous. 
. Mr. Darwin rejects the notion that Natural Selection has favoured self-sterility in 
order to prevent self-fertilization, and finally comes to the conclusion that * we must 
look at it as an incidental result." Now this somewhat tallies with his modified views 
respecting Nature that she ** abhors perpetual self-fertilisation." He remarks (J. c. p. 8), 
* If the word perpetual had been omitted, the aphorism would have been false. As it 
stands, I believe that it is true, though perhaps rather too strongly expressed." Mr. 
Meehan goes further, and I am prepared to go with him; for that observer remarks :— 
SECOND SERIES.—BOTANY, VOL. I. SA 
H 
