202 



SCIENTIFIC NEWS. 



[Aug. 31, 1888. 



organic species gives out some peculiar scent, we are still 

 very much at a loss. Much good work has, indeed, been 

 done of late years in explaining the use of the odours 

 of certain flowers in attracting insects whose 

 visits are essential to their fecundation. The results of 

 such investigations will, of course, be familiar to most 

 of our readers. But there are in this connection a 

 multitude of unsolved questions, and to these we wish 

 to direct the attention of young naturalists as a fruitful 

 field for study and observation. 



In the first place, there are flowers not a few of which 

 give off scents ranging from the slightly disagreeable to 

 the positively loathsome. There are the sickly smell of 

 the common elder blossom or the sunflower, the 

 peculiar bitter — we use this term for want of one more 

 definite — of most of the Compositae, such as the dahlia, 

 the common marigold, the African marigold, and in 

 a more intense degree Coreopsis Drummondi ; the 

 indescribably fetid exhalation of certain Aroids, and of a 

 giant Bulbophyllum referred to in our recent article on 

 orchids. What function do these smells subserve ? Are 

 they, like perfumes, to attract some insect which may 

 convey the pollen of one flower to the pistil of another, 

 and thus promote fecundation ? If so, what insect ? 

 Certainly no bee or butterfly. The likings of these 

 insects as regards odours are admittedly not like our 

 own. We see both butterflies and bees preferring the 

 sugary but sickly aroma of the privet, the African sedum, 

 the sweet marjoram, and the prickly comfrey to the 

 delicious fragrance of the syringa, the orange-blossom, or 

 the lavender. But for all this none of them, as far as 

 we have observed, like positive stenches. 



In some cases flowers seem to find their advantage in 

 smelling like carrion. Blow-flies are seduced, as may 

 be found mentioned in the text-books, into depositing 

 their eggs in such flowers. The young grubs perish as 

 a matter of course, and the flower, in some manner 

 which requires further investigation, preys upon their 

 remains. But many evil-smelling flowers do not in theleast 

 remind us of putrid animal matter, and in fact have 

 not been seen to be visited by blow-flies. 



Have the offensive smells been developed in order to 

 repel some enemy? If so, they often fail. Every 

 gardener knows, for instance, that the destructive ear- 

 wig is found as abundantly in the disagreeably-smelling 

 dahlia, sunflower, or marigold as in the fragrant carna- 

 tion or white lily. 



Then we have to consider the smells, good or bad, 

 proceeding not from the flowers of any plant, but from 

 the fruits, the leaves, the stem, or the roots. Here the 

 fecundation of the seed and the prevention of self-ferti- 

 lization do not come into any direct play. Not a few 

 plants have altogether very agreeable odours. Of these, 

 the sweet briar is the most familiar instance. What 

 advantage, if any, does it gain in comparison with other 

 members of the great rose family by the fragrance 

 which pervades its leaves and its shoots ? So far " the 

 oracles are dumb." On the opposite side we have plants 

 which give out a more or less disagreeable smell, 

 especially when crushed, such as the so-called dead 

 nettle. But the function of this and similar unpleasant 

 scents, e.g., that of the leaves of the common scarlet 

 geranium, is still a matter of doubt. The odours of a 

 number of plants, such as thyme, mint, and lavender, 

 have been explained as protective, not against insects 

 but against cold. The scents of such plants, indeed of 

 the Labiates generally, are due to essential oils, which 



being very volatile, constantly envelope the plants in an 

 atmosphere which hinders them from losing heat by 

 radiation in a chilly night as readily as it would other- 

 wise be the case. This explanation is the more probable, 

 as the Labiates for the most part are intolerant of frost. 



Another explanation of the smells of parts of plants 

 other than the flowers, is that they are intended to attract, 

 or respectively to repel, animals which might eat such 

 parts. We may easily conceive that it might suit the — 

 of course unconscious — purposes of a plant that its fruits 

 should be eaten by some kinds of animals and not by 

 others. If ^consequently it develops a scent which 

 attracts the former and repels the latter, it may find a 

 benefit. Now, a scent good or bad will have this effect, 

 and as all animals do not approve of the same kinds of 

 scents, the effect will possibly be selective. If the 

 question be raised why it should make any difference to 

 the plant by what animal its fruits are consumed, the 

 answer is not far to seek. One species may swallow 

 the seeds unbruised, and may afterwards excrete them 

 uninjured. In this manner their dispersion will be pro- 

 moted, and each will be accompanied by matter which 

 will promote its germination and growth. Another fruit- 

 eating species, e.g., rodent mammals, may gnaw the seed 

 to fragments, especiallyif large, or may swallow it whole 

 or in pieces and digest it, as do many birds. It is plain 

 that to be eaten in this manner is a hindrance to the per- 

 petuation of any vegetable species. 



It must be remembered that the smell of a fruit or 

 other part of a plant does not by any means invariably 

 give a clue to its taste. Thus the smell may be more or 

 less repellent, but if this warning be neglected the taste 

 may prove pleasant. The most striking instance of this 

 is the durrian, of the Malay Islands. 



Every stranger, on his first contact with this fruit, 

 loathes its smell, and we believe every one who makes 

 the experiment finds its taste delightful. 



A less striking, though unquestionable case, is that of 

 the onion family, universally denounced for their smell, 

 but almost as universally eaten. Farmers are often 

 annoyed at the avidity with which their cows will browse 

 the wild onion, if accessible, thus injuring the flavour of 

 the milk and butter. The smell of the onion is thus no 

 protection. 



On the other hand, a pleasant odour may accompany a 

 very unpleasant taste. In decoctions of certain very 

 bitter roots, such as gentian and calumba, a fruity odour 

 may usually be perceived. What can be the purpose of 

 the smell ? 



Very many kinds of trees and shrubs when first 

 coming into leaf, and before the flowers appear, have a 

 decidedly pleasant odour. Prominent in this respect are 

 the Canada poplar, the pines when putting out fresh 

 growths, the birch and the oak. Here, again, we do 

 not know what purpose is thus served. 



It is not easy to imagine how a plant of any kind can 

 be benefited by having its leaves or sprouts eaten away, 

 whether by cattle, rabbits, locusts, cockchafers, or slugs. 

 Yet odours which effectually repel such attacks are very 

 rare. 



To conclude with an irrelevant and, we fear, un- 

 answerable question, we must ask whether the snails 

 and slugs were originally consumers of dead and decay- 

 ing ' vegetable matter, and have since extended their 

 ravages to healthy leaves, fruits, and flowers, or whether 

 they were originally devourers of fresh plants, and have 

 subsequently taken to eating vegetable refuse ? 



