284 BOTANY 



stimulus of hunger, plants utilise the reproductive instinct of animals 

 for securing their pollination. Not a few plants (Stapelia, Aristolochia, 

 and members of the Araceae), by the unnatural colour of their flowers, 

 combined with a strong carrion-like stench, induce carrion-flies to visit 

 them and deposit their eggs; in so doing they effect, at the same time, the 

 pollination of the flowers. In South America, instead of insects, it is 

 the humming-birds which are especially active in the conveyance of 

 pollen. In addition to such Ornithophilous Plants whose pollination 

 is accomplished through the agency of birds (Marcgravia nepenthoides, 

 and different species of Feijoa and Abutilon), pollination in some cases 

 is effected by means of snails (Malacophilous Plants). To their 

 instrumentality the flowers of Galla palustris, Chrysosplenium, and also the 

 half-buried flowers of the well-known Aspidistra owe their pollination. 



Self and Cross Fertilisation. — It has already been pointed out 

 that it is by sexual reproduction, in contrast to the vegetative mode 

 of multiplication, that qualitative modifications are effected. Such 

 qualitative changes are best attained when the sexual cells are derived 

 from different individuals ; although, when they spring from the same 

 individual, through the recurrence of ancestral characteristics (atavism, 

 p. 277), there is always the possibility of the appearance of descendants 

 which differ greatly from those produced vegetatively, by the same 

 plant. By such close fertilisation, however, no opportunity is given 

 for a new blending with others of the same species. It is an old 

 maxim founded on experience, that prolonged close-breeding produces 

 a deteriorating effect, as the slightly injurious variations, which other- 

 wise would have been equalised by cross-breeding, become augmented. 

 It is in accordance with this same principle that, in the sexual 

 reproduction of plants, varied and often complicated contrivances are 

 manifested, which conduce to CROSS -fertilisation (union between 

 sexual cells of different individuals), even when the individuals them- 

 selves are hermaphrodite and possess two kinds of sexual organs, 

 as in the case of the majority of Phanerogams. 



As, however, self -fertilisation takes place also in a small number 

 of plants, either regularly or from necessity, it is evident that what- 

 ever may be the advantage derived from a union of two distinct 

 individuals, it is no more essential for sexual reproduction than for 

 vegetation multiplication. Though in consideration of the otherwise 

 predominant tendency to cross-fertilisation, self-fertilisation, just as 

 apogamy, appears to be a retrogression. Self-pollination, although 

 regularly occurring, frequently fails to occasion self-fertilisation, as 

 often the pollen will not develop pollen-tubes on the stigmas of the 

 flower (self-sterile) by which it was produced, but only on those of 

 different flowers (Secale cereals, Gorydalis cava, Lobelia fulgens, Verbascum 

 nigrum, etc.). 



The antipathy between the sexual organs of the same flower, in certain plants, 

 so greatly exceeds the bounds of indifference that they act upon each other as 



