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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