SPARE HALF HOURS.

Otago Witness, Issue 1900, 3 July 1890, Page 41

SPARE HALF HOURS.

Br F. A. Joseph.

DESIGN IN NATURE. 11. The most wonderful designs for securing the cross-fertilisation of plants are to be witnessed in the mechanisms of the reproductive organs of some orchids. Orchis pyramidalis is one of the most common orchids. Of the fertilisation of this flower Mr A. R. Wallace writes:— "The broad trifid lip of the flower offers a support to the moth, which is attracted by its sweet odour, and two ridges at the base guide tho proboscis with certainty to the narrow entrance of the nectary. When the proboscis has reached the end of tho spur its basal portion depresses the little hinged nostellum that covers the saddle-shaped sticky glands to which the pollen masses are attached. On the proboscis being withdrawn, tho two pollonia (pollen bearers) stand erect and parallel, firmly attached to the proboscis. In thi3 position, however, they would be useless, as they would misu the stigmatic surface of tho next flower visited by tho moth. But as soon as the proboscis is withdrawn the two pollen masses begin to diverge till they are exactly as far apart as are the stigmas of the flower ; and then commences a second movement which brings them down till they project straight forward nearly at right angles to their first position, so as exactly to hit against the stigmatic surface of the next flower visited, on which they leave a portion of their pollen. The whole oE these motions take about half a minute, and in that time the moth will usually have flown to another plant, and thus effect the most beneficial kind of cross-fertilisation.' 1 The wonderful mechanisms of this flower and the contrivance whereby the insect carries off the entire pollen masses on its proboscis, and the almost lifelike movements of the pollen masses to bring them into the correct position for fertilising the next flower visited by the moth, surely irnplie design. One other instance, related by Dr Cruger and mentioned in Darwin's " Fertilisation, of Orchida," must suffice to illustrate what are, perhaps, the most complicated examples of contrivances to ensure the cross-fertilisation of plants. This orchid (coryanthes) " has part of its labellura, or lower lip, hollowed out into a great bucket, into which drops of almost pure water continually fall from two secreting horns which stand above it ; and when the bucket is half full the water overflows by a spout on one side. Tho basal part of the labellum stands over the bucket, and is itself hollowed out iuto a soifc of chamber with two lateral entrances ; within this chamber there are curious flashy ridges. The most ingenious man, if he had not witnessed what" takes place, could never Lave imagined what purpose all these parts serve. But Dr Oruger saw crowds of large humbte bees visiting the gigantic flowers of this orchid, not in order, to suck the nectar, but to gnaw off the ridges within the chamber above the bucket. In doing this they frequently pushed each other into the bucket, and their wings being thus wetted they could not fly, but were compelled to crowd out by the oassage formed by the spout or overflow. Dr Oruger^saw a continued procession of bees thus crawling out of their involuntary bath. The passage is nanow and roofed over by the column, so that a bee, iv forcing its way out, first rubs its back against the viscid stigma and then against the viscid glands of the pollen masses. The pollen masses are thus glued to the back of the bee which first happens to crawl out through the passage of a lately- expanded flower, and are thus carI ried away. When the bee, thus provided, flies to another flower, or to the same flower a second time, and is pushed by its ; comrades into the bucket, and then crawls out by the passage, the pollen mass necessarily comes first into contact with the viscid stigma and adheres to it, and the flower is fertilised. Now we see the use of every part of the flower, of the water-secreting horns, of the bucket half full of water, which .prevents the bees from flying away and forces them to crawl out through the spout and rub against the properly-placed viscid pollen masses and the viscid stigma." Here the design is as striking as it is effective. We cannot examine these complex mechanisms without seeing their purpose, and_ wondering why simpler means were not provided, as in the case of such simple flowers as the buttercup or dog rose, were it not that we know why these things were designed. Nature demands cross-fertilisation ; insects are the most suitable agents, therefore flowers are so designed as to attract insects. Design could not be more apparent, and surely no one will deny the omniscient wisdom of the Designer. The brilliant flowers that deck the field or beautify the landscape bloom not, then, in vain; their sweetness is not " wasted on the desert air," and they do not "blush unseen." Their brilliant petals have been specially designed to attract passing insects ; or, if the petals be sober-hued, a ; rich perfume tells the winged wanderer where to seek for nectar, for in Nature everything displays the highest utility, and nothing Hiat has been made is without a purpose. Olose observers have noticed that in a single genus of plants (geranium) the more conspicuously flowered kinds were visited by twice as many different species of insects as were the less conspicuous kinds. Professor Muller, after many years of patient observation, came to the conclusion that " a species of flower is the more visited by insects the more conspicuous it is." Sweet odour is almost invariably supplementary to brilliant colour, and is rarely present in the largest and most gaudily coloured flowers, which habitually grow in open situations. Where both are combined the flower 3 usually grow in secluded localities, when the sweet scent is certain to attract passing insects, even if they do not paes near enough to see the flower. The sweetest scent often belongs to the least conspicuousjflowers, as in the case of the mignonette, which readily attracts bees by its delicious odour. It is found that white flowers are often fertilised by moths, and, in adaptation to the nocturnal habits of these insects, give out their scent only by night; and some of these flowers only open at night. Such flowers aro generally long-tubed, in accordance with the length of the probosoeg of these iusects.