400 
TROHCAL NATURE 
VI 
small brown seeds. Others whose seeds are ejected by the 
bursting open of their capsules, as with the oxalis and many 
of the caryophyllacese, scrophulariacese, etc., have their seeds 
very small and rarely or never edible. 
It is to be remarked that most of the plants whose large- 
seeded nuts cannot be eaten without destroying their germ- 
inating power — as the oaks, beeches, and chestnuts — are 
trees of large size which bear great quantities of fruit, and 
that they are long lived and have a wide geographical range. 
They belong to what are called dominant groups, and are 
thus able to endure having a large proportion of their seeds 
destroyed with impunity. It is a suggestive fact that they 
are among the most ancient of known dicotyledonous plants — 
oaks and beeches going back to the Cretaceous period with 
little change of type, so that it is not improbable that they 
may be older than any fruit-eating mammal adapted to feed 
upon their fruits. The attractive coloured fruits on the other 
hand, having so many special adaptations to dispersal by 
birds And mammals, are probably of more recent origin . 1 
The apple and plum tribes are not known earlier than the 
Miocene period ; and although the record of extinct vegetable 
life is extremely imperfect, and the real antiquity of these 
groups is no doubt very much greater, it is not improbable 
that the comparative antiquity of the fruit-bearing and nut- 
bearing trees may remain unchanged by further discoveries, 
as has almost always happened as regards the comparative 
antiquity of animal groups. 
Attractive Colours of Flowers 
The colours of flowers serve to render them visible and 
recognisable by insects, which are attracted by secretions of 
nectar or pollen. During their visits for the purpose of 
obtaining these products, insects involuntarily carry the 
pollen of one flower to the stigma of another, and thus effect 
cross -fertilisation, which, as Mr. Darwin was the first to 
demonstrate, immensely increases the vigour and fertility of 
the next generation of plants. This discovery has led to 
the careful examination of great numbers of flowers, and the 
1 I owe this remark to Mr. Grant Allen, author of Physiological 
^Esthetics. 
