XI 
THE SPECIAL COLOURS OF PLANTS 
329 
form. With these modifications the species might extend its 
range into new districts, thereby obtaining increased vigour 
by the change of conditions, as appears to have been the case 
with so many of the small flowered self-fertilised plants. Thus 
it might continue to exist for a long series of ages, till under 
other changes—geographical or biological—it might again 
suffer from competition or from other adverse circumstances, 
and be at length again confined to a limited area, or reduced 
to very scanty numbers. 
But when this cycle of change had taken place, the species 
would be very different from the original form. The Mower 
would have been at one time modified to favour the visits 
of insects and to secure cross-fertilisation by their aid, and 
when the need for this passed away, some portions of these 
structures would remain, though in a reduced or rudi¬ 
mentary condition. But when insect agency became of 
importance a second time, the new modifications would 
start from a different or more advanced basis, and thus a 
more complex result might be produced. Owing to the 
unequal rates at which the reduction of the various parts 
might occur, some amount of irregularity in the flower might 
arise, and on a second development towards insect cross¬ 
fertilisation this irregularity, if useful, might be increased by 
variation and selection. 
The rapidity and comparative certainty with which such 
changes as are here supposed do really take place, are well 
shown by the great differences in floral structure, as regards 
the mode of fertilisation, in allied genera and species, and even 
in some cases in varieties of the same species. Thus in the 
Ranunculacese we find the conspicuous part of the Mower to be 
the petals in Ranunculus, the sepals in Helleborus, Anemone, 
etc., and the stamens in most species of Thalictrum. In all 
these we have a simple regular flower, but in Aquilegia it is 
mad-e complex by the spurred petals, and in Delphinium and 
Aconitum it becomes quite irregular. In the more simple class 
self-fertilisation occurs freely, but it is prevented in the more 
complex Mowers by the stamens maturing before the pistil. 
In the Caprifoliacese we have small and regular greenish 
Mowers, as in the moschatel (Acloxa); more conspicuous regular 
open Mowers without honey, as in the elder (Sambucus); and 
