from the tip; which, when the insect subsequently visited a long-styled flower, would again come just opposite to the head of the pistil. Hence we see that by this beautiful arrangement insects must carry the pollen of the long-styled form to the short-styled, and vice versâ.

The economy of pollen is not the only advantage which plants derive from these visits of Insects. A second and scarcely less important is that they tend to secure "cross fertilisation"; that is to say, that the seed shall be fertilised by pollen from another plant. The fact that "cross fertilisation" is of advantage to the plant doubtless also explains the curious arrangement that in many plants the stamen and pistil do not mature at the same time- the former having shed their pollen before the pistil is mature; or, which happens less often, the pistil having withered before the pollen is ripe. In most Geraniums, Pinks, etc., for instance, and many allied species, the stamens ripen first, and are followed after an interval by the pistil.

THE NOTTINGHAM CATCHFLY

The Nottingham Catchfly (Silene nutans) is a very interesting case. The flower is adapted to be fertilised by Moths. Accordingly it opens towards evening, and as is generally the case with such flowers, is pale in colour, and sweet-scented. There are two sets of stamens, five in each set. The first evening that the flower opens one set of stamens ripen and expose their pollen. Towards morning these wither away, the flower shrivels up, ceases to emit scent, and looks as if it were faded. So it remains all next day. Towards evening it reopens, the second set of stamens have their turn, and the flower again becomes fragrant. By morning, however, the second set of stamens have shrivelled, and the flower is again asleep. Finally on the third evening it re-opens for the last time, the long spiral stigmas expand, and can hardly fail to be fertilised with the pollen brought by Moths from other flowers.

THE HEATH

In the hanging flowers of Heaths the stamens form a ring, and each one bears two horns. When the Bee inserts its proboscis into the flower to reach the honey, it is sure to press against one of these horns, the ring is dislocated, and the pollen falls on to the head of the insect. In fact, any number of other interesting cases might be mentioned.

BEES AND FLIES

Bees are intelligent insects, and would soon cease to visit flowers which did not supply them with food. Flies, however, are more stupid, and are often deceived. Thus in our lovely little Parnassia, five of the ten stamens have ceased to produce pollen, but are prolonged into fingers, each terminating in a shining yellow knob, which looks exactly like a drop of honey, and by which Flies are con

tinually deceived. Paris quadrifolia also takes them in with a deceptive promise of the same kind. Some foreign plants have livid. yellow and reddish flowers, with a most offensive smell, and are constantly visited by Flies, which apparently take them for pieces of decaying meat.

The flower of the common Lords and Ladies (Arum) of our hedges is a very interesting case. The narrow neck bears a number of hairs pointing downwards. The stamens are situated above the stigma, which comes to maturity first. Small Flies enter the flower apparently for shelter, but the hairs

a

Fig. 14.-Arum.

prevent them from returning, and they are kept captive until the anthers have shed their pollen. Then, when the Flies have been well dusted, the hairs shrivel up, leaving a clear road, and the prisoners are permitted to escape. The tubular flowers of Aristolochia offer a very similar case.

PAST HISTORY OF FLOWERS

If the views here advocated are correct, it follows that the original flowers were small and green, as wind-fertilised flowers are even now. But such flowers are inconspicuous. Those which are coloured, say yellow or white, are of course much more visible and more likely to be visited by insects. I have elsewhere given my reasons for thinking that under these circumstances some flowers became yellow, that some of them became white, others subsequently red, and some finally blue. It will be observed that red and blue flowers are as a rule highly specialised, such as Aconites and Larkspurs as compared with Buttercups; blue Gentians as compared with yellow, etc. I have found by experiment that Bees are especially partial to blue and pink.

Tubular flowers almost always, if not always, contain honey, and are specially suited to Butterflies and Moths, Bees and Flies. Those which are fertilised by Moths generally