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400 TROPICAL NATUREsmall brown seeds. Others whose seeds are ejected by thebursting open of their capsules, as with the oxalis and manyof the caryophyllacese, scrophulariacese, etc., have their seedsvery small and rarely or never edible.It is to be remarked that most of the plants whose largeseedednuts cannot be eaten without destroying their germinatingpower as the oaks, beeches, and chestnuts aretrees of largesize which bear great quantities of fruit, andthat they are long lived and have a wide geographical range.They belong to what are called dominant groups, and arethus able to endure having a large proportion of their seedsdestroyed with impunity. It is a suggestive fact that theyare among the most ancient of known dicotyledonous plantsoaks and beeches going back to the Cretaceous period withlittle change of type, so that it is not improbable that theymay be older than any fruit-eating mammal adapted to feedupon their fruits. The attractive coloured fruits on the otherhand, having so many special adaptations to dispersal bybirds and mammals, are probably of more recent origin. 1The apple and plum tribes are not known earlier than theMiocene period ;and although the record of extinct vegetablelife is extremely imperfect, and the real antiquity of thesegroups is no doubt very much greater, it is not improbablethat the comparative antiquity of the fruit-bearing and nutbearingtrees may remain unchanged by further discoveries,as has almost always happened as regards the comparativeantiquity of animal groups.Attractive Colours of FlowersThe colours of flowers serve to render them visible andrecognisable by insects, which are attracted by secretions ofnectar or pollen. During their visits for the purpose ofobtaining these products, insects involuntarily carry thepollen of one flower to the stigma of another, and thus effectcross -fertilisation, which, as Mr. Darwin was the first todemonstrate, immensely increases the vigour and fertility ofthe next generation of plants. This discovery has led tothe careful examination of great numbers of flowers, and the1 I owe this remark to Mr. Grant Allen, author of PhysiologicalEsthetics.