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Black bulbuls, like sunbirds, get well dusted with pollen while diving into flowers after nectar, and so probably act the part of insects as regards the cross-fertilisation of large flowers. In respect of nesting habits, black bulbuls conform more closely to the ways of their tribe than they do in other matters. The nesting season is early spring.
During this autumn of 1876 I shall publish on the 'Effects of Cross and Self-Fertilisation in the Vegetable Kingdom. This book will form a complement to that on the 'Fertilisation of Orchids, in which I showed how perfect were the means for cross-fertilisation, and here I shall show how important are the results.
The weight of this objection is obvious; but our ignorance of the conditions of fertility and sterility, the want of carefully conducted experiments extending over long series of years, and the strange anomalies presented by the results of the cross-fertilisation of many plants, should all, as Mr. Darwin has urged, be taken into account in considering it. The eighth and last stands as follows:
The book bears somewhat the same relation to my little book on 'Climbing Plants, which 'Cross-Fertilisation' did to the 'Fertilisation of Orchids; for in accordance with the principle of evolution it was impossible to account for climbing plants having been developed in so many widely different groups unless all kinds of plants possess some slight power of movement of an analogous kind.
Creighton insists chiefly on the importance of change, which though I did not notice his saying so he would doubtless see as a mode of cross-fertilisation, fraught in all respects with the same advantages as this, and requiring the same precautions against abuse; he would not, however, I am sure, deny that there could be no fertility of good results if too wide a cross were attempted, so that I may claim the weight of his authority as supporting both the theory of an unconscious memory in general, and the particular application of it to medicine which I had ventured to suggest.
If any approach to sterility occurred in mongrels between these it would be a grand step. The most curious point you have brought out seems to me the slight superiority of self-fertilisation over fertilisation with another flower of the same plant, and the most important result, that difference of constitution is the essence of the benefit of cross-fertilisation.
He sent me some seeds, and on raising some plants I was so much fascinated and perplexed by the revolving movements of the tendrils and stems, which movements are really very simple, though appearing at first sight very complex, that I procured various other kinds of climbing plants and studied the whole subject.... Some of the adaptations displayed by climbing plants are as beautiful as those of orchids for ensuring cross-fertilisation."
If carried to its logical conclusion, such a cosmopolitan broad-mindedness, such a cross-fertilisation of intellectual products, must give rise to the ennobling idea that there is only one truth, and that the external forms are only fleeting waves upon the vast ocean of human ideals. The attempt was made in Alexandria by the Judæo-Hellenic philosophers.
Cross-fertilisation is just as necessary for continued fertility of ideas as for that of organic life, and the attempt to frown this or that down merely on the ground that it involves contradiction in terms, without at the same time showing that the contradiction is on a larger scale than healthy thought can stomach, argues either small sense or small sincerity on the part of those who make it.
It is proper to add that this view has been sharply challenged by a number of recent writers. It is questioned if colours and scents do attract insects; though several recent series of experiments seem to show that bees are certainly attracted by colours. It is questioned if cross-fertilisation has really the importance ascribed to it since the days of Darwin.
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