SPARE HALF HOURS.

Otago Witness, Issue 1901, 10 July 1890, Page 34

SPARE HALF HOURS.

By F. A. Joseph.

DESIGN IN NATURE. 111.

It is found that bright red flowers are specially attractive to butterflies, and many such are specially adapted to be fertilised by them, while bees are considered to be specially attracted by blue flowers, although they, in common with other nectar-loving insects, frequent flowers of all colours. Flies are attracted by flowers of a dull yellow colour, which have a special attraction often enough for these insects in possessing a carrion-like smell ; and there are other flowers which possess special attractions for wasps. The rule all along the line is, that where it is necessary to the continued existence of the speciea that insects should secure crossfertilisation, the flower is specially attractive to such insects as can best meet the plant's needs. But it must be borne in mind that the flower is beautiful, or sweet-scented, or malodorous, because there are insect tastes to please, and because it is required that plants should be cross-fertilised. Yet there are flowers with neither scent nor nectar, and these never would be visited by insects but for the fact that they possess sham nectaries 1 In one well known plant the ovary glistens as if moist, and flies, deluded by the sham, alight on it and carry away pollen to another plant, while in another there are a number of little yellow balls near the base of the flower which look like drops of honey, but are in reality dry. The insect accustomed to find nectar in other flowers is easily deceived by the sham nectary, and 60 the work of cross-fertilisation goes on. In time experience will teach these industrious little workers to avoid these flowers, for even insects possess a degree of intelligence sufficient for that, but a young race of other insects who have to learn de now will continue the necessary work. The slight loss of time entailed upon young insects in visiting flowers useless to them does not do outrage to the general economy of Nature to any appreciable extent ; and if it does there is more than a compensation elsewhere. The time spent in visiting flowers that have been already fertilised would be quite wasted, so we find that in a great many flowers the colour changes as soon as they are fertilised.

The common lungwort is at first red, but at a later stage turns blue. Now, it has been observed that the bees freely visited the red flowers, while the blue ones were passed by. There is a plant in Brazil whose flowers are yellow the first day, orange the second, and purple the third. Butterflies visit the yellow flowers freely, some visit the yellow and the orange flowers, but none have been observed to visit the purple flowers. The latter having already been fertilised, no longer require insect visits, and their colour warns the little workers that such visits would be made in vain.

The question of insect fertilisation being one of supply as well as demand, we find that generally flowers are modified in any locality to suit the insects that there abound. Taking a common plant, the gentian, it is worthy of note that those growing on low lands are adapted for fertilisation by bees, while those of the high Alps are adapted for butterflies only. Bees seldom visit these highlands, while butterflies abound. Butterflies can get at the neotar of flowers adapted for fertilisation by bees without crossfertilising them ; therefore there must be a modification of the flower to suit the requirements of the case. The adaptation is marvellously complete, however it may have been brought about. There are those who claim that in these wonderful molifications of structure we see nothing more than conformity to the ordinary laws of growth. That is something like Topsy's reason when asked who made her. The flowers on the lowlands and on the highlands have probably each responded to the same laws of growth, yet in the one case they are fertilised by bees and in the other by butterflies only— there is a discriminating principle somewhere.

I have more than once referred to economy in Nature. Economy of time is important to both insects and flowers, as fine days are as essential to the honey gatherer as to the flowers ripe for fertilisation. Consequently we might expect, as has been testified by many careful observers, that many kinds of nectar-loving insects, and more especially bees, keep to one kind of flower at a time, visiting hundreds of similar blossoms in succession. Whether the bee in the interval between leaving the hive and returning with its burden keeps to one kind of flower, or how long it continues so to act, has not yet been placed on record. It would be interesting to know, if such could be ascertained, whether a single cell is filled by one bee, and whether that particular cell is filled with honey from a certain kind of flower, thus compelling the bee to carry on the work of cross-fertilisation with certainty. In any case those bees keeping to a certain kind of flower will soon acquire quickness in going direct to the nectary, and thus time will be saved, so making the needß of the flower subservient to those of the insect. To meet the requirements of both flower and insect, those flowers that bloom intermingled at the same season of the year are generally very distinct,

both in form and oolour. Here we have economy again, and the insects have no difficulty in going direct to the flower they want, even where there is a profusion of bloom of other kinds.

So far a running sketch of the part played by insects in the cross-fertilisation of plants has carried us. The sketch has necessarily been meagre in outline; those who desire to pursue this highly interesting subject must consult some of the works dealing with, the fertilisation of plants. I cannot do better than conclude this part of my sketch by quoting from two distinguished men. Darwin wrote in his " Origin of Species" :— " Hence we may conclude that if insects had not been developed on the earth our planet would not have been decked with beautiful flowers, but would have produced only such poor flowers as we see on our fir, oak, nut, and ash trees, or grasses, docks, and nettles, which are all fertilised through the agency of the wind." Mr Grant Allen writes : "While man has only tilled a few level plains, a few great river valleys, a few peninsular mountain- slopes, leaving the vast mass of earth untouched by bis hand, the insect has spread himself over every land in a thousand shapes, and has made the whole flowering creation subservient to his daily wants. His buttercup, his dandelion, and his meadow-sweet grow thick in every English field. His thyme clothes the hillside; his heathet purples the bleak, grey moorland. High up among the alpine heights his gentian spreads its lakes of blue ; amid the snows of the Himalayas his rhododendrons gleam with crimson light. Even the wayside pond yields him the white crowfoot and the arrowhead, while the broad expanses of Brazilian streams are beautified by his gorgeous water-lilies. The insect has thus turned the whole surface of the earth into a boundless flower garden, which supplies him from year to year with pollen or honey, and itself in turn gains perpetuation by the baits that it offers for his allurement."