PDF - Wallace Online

vi COLOURS OF PLANTS 401result has been that the most wonderful and complex arrangementshave been found to exist, all having for their object tosecure that flowers shall not be self-fertilised perpetually, butthat 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 curiousphenomena have since been found to occur even among someof the most regularly -formed flowers. The arrangement,length, and position of all the parts of the flower is nowfound to have a purpose, and not the least remarkable portionof the phenomenon is the great variety of ways in whichthe same result is obtained. After the discoveries withregard to orchids, it was to be expected that the irregular,tubular, and spurred flowers should present various curiousadaptations for fertilisation by insect -agency. But evenamong the open, cup -shaped, and quite regular flowers, inwhich it seemed inevitable that the pollen must fall on thestigma and produce constant self -fertilisation, it has beenfound that this is often prevented by a physiological variationthe anthers constantly emitting their pollen either alittle earlier or a little later than the stigmas of the sameflower, or of other flowers on the same plant, were in thebest state to receive it ;and as individual plants in differentstations, soils, and aspects differ somewhat in the time offlowering, the pollen of one plant would often be conveyedby insects to the stigmas of some other plant in a conditionto be fertilised by it. This mode of securing cross-fertilisationseems so simple and easy that we can hardly help wonderingwhy it did not always come into action, and so obviate thenecessity for those elaborate, varied, and highly complexcontrivances found perhaps in the majority of colouredflowers. The answer to this of course is, that variation sometimesoccurred most freely in one part of a plant's organisationand sometimes in another, and that the benefit of cross-fertilisationwas so great that any variation that favoured it waspreserved, and then formed the starting-point of a wholeseries of further variations, resultingin those marvellousadaptations for insect fertilisation which have given much oftheir variety, elegance, and beauty to the floral world. For2D