SELF-FERTILIZATION OF PLANTS. 881 
will illustrate the former of the above degradations. Small-flowered Ranunculi have 
often less than twelve stamens; Myosurus has five; Senebiera didyma has only two; 
cleistogamous flowers of Viola canina two or three ; Stellaria media often three only, &c. 
This is in accordance with the fact that only a relatively small amount of pollen is really 
requisite for fertilization. An interesting experiment of Mr. Darwin's proves this. 
He placed a very small mass of pollen-grains on one side of the large stigma of Ipomea 
purpurea, and a great mass of pollen over the whole surface of the stigma of other 
flowers, and the result was that the flowers fertilized with little pollen yielded rather 
more capsules and seeds than did those fertilized with an excess (‘ Cross and Self- 
fertilisation,’ p. 25). That normally intercrossing flowers produce a great superfluity of 
pollen is well known. Thus Kólreuter found that sixty grains were necessary to fertilize 
all the ovules of a flower of Hibiscus, while he calculated that 4863 grains were pro- 
duced by a single flower, or eighty-one times too many (Darwin, l. e. p. 877). The 
latter says :— 
** In order to compensate the loss of pollen in so many ways, the anthers produce a far larger amount 
than is necessary for the fertilisation of the same flower. ...... and it is still more plainly shown 
by the astonishingly small quantity produced by cleistogene flowers, which lose none of their pollen, 
in comparison with that produced by the open flowers borne by the same plants; and yet this small 
quantity suffices for the fertilisation of all their numerous seeds ” (/, c. p. 376). 
Mr. Darwin observed that when flowers were artificially self-fertilized for several 
successive generations, a degeneracy sometimes took place in the anthers and pollen; 
and he seems to attribute this to the “evil effects” of self-fertilization ; but from the 
above facts I am inclined to regard it as an illustration of a universal principle in Nature, 
namely, the preservation of energy wherever possible, and that such cases as appeared 
under his experiments were adaptations to this principle, as the flowers became habi- 
tuated to self-fertilization. 
It is perhaps worthy of note that while both the number of stamens and the quantity 
of pollen are thus often much reduced in some flowers the capsules of which produce 
many seeds, yet in others which set but one, as Fumaria, or at least but few seeds, the 
number of stamens may remain unreduced. Such seems to me to be an additional proof 
that such flowers are degradations from forms originally adapted to intercrossing when 
much more pollen was requisite. Hence the present forms are retentions of former 
ancestral conditions. The following cases will illustrate this :— 
Daphne Laureola has 8 stamens and 1 seed. 
Chenopodium has . . . . . 5 » l 
Medicago, Sis has ficia yx.» 10 D lc 
Vicia tetrasperma has . . .10 » 4 seeds. 
Scleranthus perennis has . . 10 i 1 seed. 
The phenomenon called contabescence by Gartner (Anim. and Pl. under Domest. ii. 
P. 165) would seem to have its rationale in this ze cup to self-fertilization. Mr. 
Darwin observes :— 
“ The anthers are affected at a very early period in the flower-bud, and remain in the same state (with ` 
one recorded exception) during the life of the plant. The affection cannot be cured by any See = n 
Temm and is propagated by layers, cuttings, Se, ren — In MG NE SS d 
a | SECOND SERIES — areir ae pd AMET ptt, : 
