XI 
THE SPECIAL COLOURS OF PLANTS 
325 
insects, they rapidly diminish in size, lose their bright colour 
or almost wholly disappear. 1 
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 proof 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 complex structure 
of flowers evidently adapted to secure this intercrossing by 
insect agency; yet we see many of the most vigorous plants 
which spread widely over the globe, with none of these 
adaptations, and evidently 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 which 
the special arrangements for cross-fertilisation appear to have 
been a failure, since they have either been supplemented by 
special means for self-fertilisation, or have reverted back in 
various degrees to simpler forms in which self-fertilisation 
becomes the rule. There is also a further difficulty in the 
highly complex modes by which cross-fertilisation is often 
brought about; for we 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 flower; and when we consider that the result attained 
with so much cost of structural modification is by no means 
an unmixed good, and is far less certain in securing 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 now see 
whether any light can be thrown on these various anomalies 
and contradictions. 
Intercrossing not necessarily Advantageous. 
Xo one was more fully impressed than Mr. Darwin with 
the beneficial effects of intercrossing on the vigour and fertility 
1 H. Muller gives ample proof of this in his Fertilisation of Flowers. 
