466 TROPICAL NATURE 



made showing that crosses between flowers with stamens and 

 styles of unequal length were always nearly barren. During 

 these experiments 20,000 seeds of Lythrum salicaria were 

 counted under the microscope. For several years a further 

 supplementary series of experiments were carried out, show- 

 ing that the seeds produced by the illegitimate crosses (as he 

 terms them) were not only very few, but, when sown, always 

 produced comparatively weak, small, or unhealthy plants, not 

 likely to exist in competition with the stronger offspring of 

 legitimate crosses. There is thus the clearest proof that these 

 complex arrangements have the important end of securing 

 both a more abundant and more vigorous offspring. 



Perhaps no researches in the whole course of the study of 

 nature have been so fertile in results as these. No sooner 

 were they made known than observers set to work in every 

 part of the world to examine familiar plants under this new 

 aspect. With very few exceptions it is now found that every 

 flower presents arrangements for securing cross-fertilisation, 

 either constantly or occasionally, sometimes by the agency of 

 the wind, but more frequently through the mediation of 

 insects or birds. Almost all the irregularity and want of 

 symmetry in the forms of flowers, which add so much to their 

 variety and beauty, are found to be due to this cause ; the 

 production of nectar and the various nectar-secreting organs 

 is directly due to it, as are the various odours and the various 

 colours and markings of flowers. In many cases flowers which 

 seem so simply constructed that the pollen must fall on the 

 stigma and thus produce self-fertilisation, are yet surely cross- 

 fertilised, owing to the circumstance of the stigma and the 

 anthers arriving at maturity at slightly different periods, so 

 that, though the pollen may fall on the stigma of its own 

 flower, fertilisation does not result ; but when insects carry 

 the pollen to another plant the flowers of which are a little 

 more advanced, cross-fertilisation is effected. There is liter- 

 ally no end to the subjects of inquiry thus opened up, since 

 every single species, and even many varieties of flowering 

 plants, present slight peculiarities which modify to some 

 extent their mode of fertilisation. This is well shown by the 

 remarkable observations of the German botanist Kerner, who 

 points out that a vast number of details in the structure of 



