XI THE SPECIAL COLOURS OF PLANTS 325 



insects, they rapidly diminisli in size, lose their bright colour 

 or almost wholly disappear ^ 



Difficulties and Contradictions. 



The very bare summary that has now been given of the 

 main facts relating to the fertilisation of flowers, will have 

 served to show the vast extent and complexity of the inquiry, 

 and the extraordinary contradictions and difficulties which it 

 presents. We have direct jiroof of the beneficial results of 

 intercrossing in a great number of cases ; we have an over- 

 whelming mass of facts as to the varied and comjDlex structiu-e 

 of flowers evidently adapted to secure this intercrossing by 

 insect agency ; yet Ave see many of the most vigorous plants 

 Avhich spread A^adely over the globe, Avith none of these 

 adaptations, and CAddently depending on self-fertilisation for 

 their continued existence and success in the battle of life. 

 Yet more extraordinary is it to find numerous cases in Avhich 

 the special arrangements for cross-fertilisation appear to have 

 been a failiu-e, since they have either been supplemented by 

 special means for self-fertilisation, or have reverted back in 

 A^arious degrees to simpler forms in Avhich self-fertilisation 

 becomes the rule. There is also a fiu'ther difficulty in the 

 highly complex modes by which cross-fertilisation is often 

 brought about ; for Ave have seen that there are several very 

 effective yet very simple modes of securing intercrossing, 

 involving a minimum of change in the form and structure of 

 the floAver ; and Avhen we consider that the result attained 

 AAdth so much cost of structural modification is by no means 

 an unmixed good, and is far less certain in secimng the per- 

 petuation of the species than is self-fertilisation, it is most 

 puzzling to find such complex methods resorted to, some- 

 times to the extent of special precautions against the possi- 

 bility of self-fertilisation ever taking place. Let us noAV see 

 Avhether any light can be throAvn on these various anomalies 

 and contradictions. 



Intercrossing not necessarily Advantageous. 



No one Avas more fully impressed than Mr. DarAvin Avith 

 the beneficial effects of intercrossing on the vigour and fertility 



1 H. Miiller gives ample proof of this iu his Fertilisation of Flowers. 



