6 INTRODUCTION. 



and continue the species. The common Lycopodium or Club- 

 moss produces offsets which extend the area occupied by the 

 plant in every available direction ; and the same is true of the 

 tropical Selaginellas and many other flowerless or so-called 

 flowerless vegetables. 



Seeds and offsets may be considered as nature's main plan 

 of reproduction; but some plants, the common Bramble for 

 example, are not unfrequently propagated from layers; and 

 the branches and stems of many other plants readily take root 

 when trodden in the earth accidentally by the larger animals. 

 In some cases plants are propagated from cuttings in a state 

 of nature accidentally perhaps, but still not unfrequently ; as 

 when swans and other vegetable-feeding water-birds break off 

 portions of the plants on which they feed, which float away and 

 root elsewhere; or when branches and twigs are broken off by 

 high winds, and fall into moist earth and take root. We have 

 even examples of natural grafting (inarching) in nature, as shown 

 by climbing species of Ficus, or even very frequently in the 

 common Linden-tree and Ivy, where two branches, or the 

 trunk and a branch, become firmly united together. Natural 

 grafting is, however, rarely if ever employed by nature as a re- 

 productive force, but rather as a means of securing additional 

 strength or power of climbing to a stronger support. 



NATURAL HYBRIDISM. 



Hybridising and cross-breeding, although generally regarded 

 as artificial methods of propagation as used by man, are never- 

 theless very frequently employed by nature not merely to per- 

 petuate, but also to strengthen and invigorate herself. Thus 

 we see that in many plants especial provision is made to 

 prevent self-fertilisation. This is especially so in the Primrose 

 family, and also among Orchids, Yuccas, and Asclepiads, nearly 

 all of which require insect or other mechanical aid to assist in 

 their fertilisation. But while these plants cannot fertilise 

 themselves, it is often very difficult indeed to prevent cross- 

 breeding, or even hybridisation in others, of which the Cu- 

 cumber and Melon or Cabbage families serve as excellent 

 examples. In the case of the Melon, the male and female 

 organs are borne in separate flowers ; and early in the season, if 

 one variety only be grown, artificial fertilisation is often neces- 

 sary to enable the fruit to " set ; " but if two or more kinds 

 are grown, and all flower together, they set freely without any 

 aid and, as the gardener is well aware, it is next to impossible 

 to keep any particular variety true, so apt are nearly all Cucur- 



