SELF-FERTILIZATION OF PLANTS. 359 
proterandrous condition of some species, as well as the self-fertilizing condition of many 
varieties of the so-called “ Scarlet Geranium " (fig. 12). | 
Oxalis Acetosella, Mr. Darwin alludes to Michalet’s description of the cleistogamous 
flowers of this species (given in Bull. Soc. Bot. de Fr., tom. vii. 1860, p. 465), and adds 
some observations of his own (‘ Forms of Flowers,’ p.321). He quotes an observation of 
Michalet’s, that the five shorter stamens are sometimes quite aborted, a condition 
I have not met with myself, but one quite in keeping with the common process of 
reduction of stamens in self-fertilizing flowers. He also adds this interesting observa- 
tion, * In one case the tubes, which ended in excessively fine points, were seen by me 
stretching upwards from the lower anthers towards the stigmas, which they had not as 
yet reached. My plants grew in pots, and long after the perfect flowers had withered 
they produced not only cleistogamic but a few minute open flowers, which were 
in an intermediate condition between the two kinds." This last remark is clearly in 
. accordance with the true origin of these flowers, that they are in all cases degradations 
from the conspicuous forms normally characteristic of the genera which produce them. 
The figs. 134, b, c, d, Tab. XLIV., clearly show that in Qzalis Acetosella the cleistogamous 
state is simply a normal flower-bud, which has become adapted to self-fertilization; and 
the intermediate conditions alluded to by Mr. Darwin I should suspect were analogous 
to the permanent forms of flowers of O. corniculata, which I at first inferred, from its 
wide distribution, must be habitually self-fertilizing *, and subsequently I discovered the 
pollen-tubes' penetrating the stigma of each unopened bud (fig. 14). M. E. Michalet's 
description (/. c. p. 467) is much to the point, as the subjoined free translation testifies. 
The cleistogamous flowers are about the size of the head of a pin, often subterranean, on short curved 
peduncles, with included petals. They arise from the same points of the rhizome, but not simul- ` 
taneously, and continue through summer and even to autumn. The sepals are closely applied during 
fertilization, and conceal hermetically the essential organs. They increase to double their size; but the 
capsule soon takes on a relatively enormous size, considering the minuteness of the ovary. The petals, 
5, are shorter than the sepals ; they rarely are wanting. The andrecium is composed of 10 stamens; 5 
are large, inserted upon a narrow disk which surrounds the base of the ovary. The anthers of the 
smaller stamens appear infertile, or even entirely abortive. The 5 fertile stamens are inclined towards 
the stigmas, and are bound to them by fine threads; they certainly play some part in the fecundation ; 
but the nature of their functions is obscure. [Consult Tab. XLIV. fig. 13d.] As in Violets, I have 
vainly looked to find the emission of the pollen from the anthers upon the stigmas. The pollen appears 
to be slightly deliquescent ; the cells which contain it have seemed to me to remain closed and intact 
after fecundation has already taken place, and is manifested by the growth of the capsules. In a very 
young ovary the 5 carpellary leaves are nearly free, as in Sedum ; later the carpels unite by their lateral 
walls and form a 5-celled ovary. The stigmas (which in the spring flowers are on long styles) are sessile 
on the ovary. The capsule is shorter and more rounded at the summit. The seeds do not appear to 
* While examining O. Acetosella I found the petioles of the leaves articulated near to, but not absolutely at the 
base. ‘The small thickened portion which remains has its cellular tissue highly charged with very large starch- 
grains. Dr. Masters tells me that this also occurs at the bases of other deciduous leaf-stalks, apparently as nutri- 
ment for the formation of the cells which give rise to the transverse division which causes the leaf to fall; but in the: 
case of the Wood-Sorrel the leaf Aas fallen, so that they must be regarded as little reservoirs of nutriment for some ` 
* 
