308 BOTANY PART i 



CONRAD SPRENGEL first pointed out in 1793 in his famous work on 

 the structure and fertilisation of flowers ("Das entdeckte Geheimniss 

 der Natur im Bau und in der Befruchtung der Blumen "), that the 

 pollen grains must necessarily become attached to certain parts of 

 the body of the animal visiting it in search of food, and so be con- 

 veyed to the sticky or hairy stigma of other flowers. The variety of 

 means employed to secure pollination, and the wonderful adaptation 

 shown by the flowers to the form and habits of different insects, are 

 most remarkable. 



In addition to the stimulus of hunger, plants utilise the reproductive instinct 

 of insects for securing their pollination. Not a few plants (Stapelia, Anstolochia, 

 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 the well-known hollow, pear-shaped inflorescences of the Fig (Ficus carica, 

 Fig. 575), there occur, in addition to long-styled female flowers that produce seeds, 

 similar gall-flowers with short styles. In each of the latter a single egg is laid by 

 the Gall -wasp (Blastophaga), which in effecting this pollinates the fertile flowers 

 with pollen carried froin the male inflorescence (the Caprificus). The large white 

 flowers of Yucca (Fig. 493) are exclusively pollinated by the Yucca moth (Pronuba). 

 The moth escapes from the pupa in the soil at the time of flowering of Yucca and 

 introduces its eggs into the ovary by means of the style ; in doing this it carries 

 pollen to the stigma. The larvae of the moth consume a proportion of the ovules 

 in the ovary, but without the agency of the moth no seeds would be developed, as 

 the sterility of the plant in cultivation shows. 



In South America the humni ing-birds are especially active in the conveyance 

 of pollen, as they seek for insects in the flowers ; a starling visits the flowers of 

 species of Puya to drink the watery nectar. In the Old World the honey-birds 

 play a similar part. MARLOTH enumerates about forty ornithophilous plants from 

 the South African flora ; these are mostly pollinated by species of Nectarinia. 

 Species of Feijoa have sweet succulent perianth leaves to attract the birds, which 

 serve to convey the pollen. 



Besides these ORNITHOPHILOUS plants there are a few visited by Bats 

 (CHIROPTEROPHILOUS) ; thus the dioecious Pandanaceous plant Freycinetia is 

 pollinated by a Flying Fox (Pteropus), which eats the inner bracts. 



Pollination in some cases is effected by means of snails (MALACOPHILOUS 

 PLANTS). To their instrumentality the flowers of Calla palustris, Chryso- 

 splenium, and also the half-buried flowers of the well-known Aspidistra owe their 

 pollination ( m ). 



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. 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 



