9o8 
PHENOMENA OF SEXUAL REPRODUCTION. 
In connection with the tendency so clearly evidenced even among Cryptogams, 
and still more among Phanerogams, to prevent self-fertilisation within the same 
hermaphrodite group of sexual organs, it is a very remarkable fact that there are a 
number of plants among Angiosperms which form two kinds of hermaphrodite 
flowers, VIZ. large flowers which can generally be fertilised by the pollen of other 
flowers, and small, more or less depauperated flowers, sometimes underground, which 
never open [Cleistogamous Flowers], the pollen emitting its tubes immediately from 
the anthers and thus fertilising the ovules. There occur therefore in these cases 
difl"erent kinds of flowers on the same individual, one kind being adapted for cross-, 
the other kind exclusively for self-fertilisation ^ This occurs, for example, in Oxalis 
Acetosella, where the small flowers are formed close to the ground when the larger 
flowers have already ripened their fruit ; in Impatiens NoH-me-tangere, Lamium 
amplexicaule^ Specularia per/oliata, many species of Viola, as V. odorata, elatior, 
cam'na, mirabilis, &c., Ruellia clandeslina, many Papilionacese, as AmphicarpcBa^ and 
Voandzeia, Commelyna bengalensis, &c. When in these cases the large typically de- 
veloped flowers are fertile, cross-fertilisation with other flowers of the same species 
must happen occasionally in the course of generations, and the small depauperated 
self-fertilised flowers then seem to be a subsidiary contrivance whose purpose is 
altogether unknown. It is however remarkable, and apparently in contradiction to 
the general rule, that the large normal flowers sometimes exhibit a tendency to infer- 
tility (as in species of Vw/a) or are altogether unfruitful (as in Voandzeia), so that 
reproduction depends in such cases mainly or entirely on the cleistogamous self- 
fertilised flowers. But since there are many questions in connection with this subject 
which find their solution in the foregoing facts, these rare exceptions cannot over- 
throw the general law^. 
In other cases, as in most Fumariaceae, Canna indica, Salvia hirta, Linum usita- 
tissimum, Draba verna, Brassica Rapa, Oxalis micrantha and sensiiiva, the pollen 
must also, according to Hildebrand, owing to the position of the sexual organs, fall 
on the stigma in the same flower, and is potent ; but in such cases, since the flowers 
are visited by insects, an occasional crossing with other flowers is not impossible. 
Even among Orchidese, where we find the most wonderful contrivances to prevent 
self-fertilisation, Darwin found an instance in Cephalanthera grandiflora in which the 
pollen-tubes are emitted from the pollen-grains on to the stigma while the former 
Rye and other cereals, see Hildebrand in Gardener s Chronicle, March 15 and 22, and May 24, 1873 ; 
also A. S. Wilson, Trans, Bot. Soc. Edin. XI. 506 and XII. 84. Flowers the pollination of which 
is effected by the wind are termed anemophilous, in contradistinction to the entomophilous, or those 
pollinated by the agency of insects.] 
^ H. V. Mohl, Einige Beobachtungen über dimorphe Blüthen, Bot. Zeit. 1863, Nos. 42, 43. 
[See also A. W. Bennett on the closed self-fertilised flowers of Impatiens in Journ, Linn. Soc. 1872, 
p. 147; ditto, Pop. Sei. Rev. 1873, p. 337. In Jiincus hufonius the pollen-tubes are emitted while 
the pollen-grains are still enclosed in the anther, perforating the wall of the latter. Henslow, On 
the Self-fertilisation of Plants, Trans. Linn. Soc, Series II, vol. I, 1879.] 
^ [Herrmann Midler (Nature, vol. VIII. p. 433 et seq.) has pointed out the existence of another 
kind of dimorphism, in which a species presents two different forms of flowers, one adapted to self- 
fertilisation, smaller and less brightly-coloured, growing in situations where there are but few 
insects, the other adapted to cross-fertilisation, larger and more brightly-coloured, growing where 
insects abound. These two forms have occasionally been described as distinct varieties or even 
species,] 
