VI COLOURS OF PLANTS 401 
result has been that the most wonderful and complex arrange- 
ments have been found to exist, all having for their object to 
secure that flowers shall not be self-fertilised perpetually, but 
that pollen shall be carried, either constantly or occasionally, 
from the flowers of one plant to those of another. Mr. 
Darwin himself first worked out the details in orchids, 
primulas, and some other groups, and hardly less curious 
phenomena have since been found to occur even among some 
of the most regularly-formed flowers. The arrangement, 
length, and position of all the parts of the flower is now 
found to have a purpose, and not the least remarkable por- 
tion of the phenomenon is the great variety of ways in which 
the same result is obtained. After the discoveries with 
regard to orchids, it was to be expected that the irregular, 
tubular, and spurred flowers should present various curious 
adaptations for fertilisation by insect-agency. But even 
among the open, cup-shaped, and quite regular flowers, in 
which it seemed inevitable that the pollen must fall on the 
stigma and produce constant self-fertilisation, it has been 
found that this is often prevented by a physiological varia- 
tion—the anthers constantly emitting their pollen either a 
little earlier or a little later than the stigmas of the same 
flower, or of other flowers on the same plant, were in the 
best state to receive it; and as individual plants in different 
stations, soils, and aspects differ somewhat in the time of 
flowering, the pollen of one plant would often be conveyed 
by insects to the stigmas of some other plant in a condition 
to be fertilised by it. This mode of securing cross-fertilisation 
seems so simple and easy that we can hardly help wondering 
why it did not always come into action, and so obviate the 
necessity for those elaborate, varied, and highly complex 
contrivances found perhaps in the majority of coloured 
flowers. The answer to this of course is, that variation some- 
times occurred most freely in one part of a plant’s organisation 
and sometimes in another, and that the benefit of cross-fertili- 
sation was so great that any variation that favoured it was 
preserved, and then formed the starting-point of a whole 
series of further variations, resulting in those marvellous 
adaptations for insect fertilisation which have given much of 
their variety, elegance, and beauty to the floral world. For 
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