402 



NA TURE 



\Scpt. 17, 1874 



12. New experiments are asked on the mode of growth of 

 bone, of such a kind as to abolish the differences of opinion 

 founded upon results apparently contradictory, announced in 

 recent years by various experimenlers. 



13. A thorough investigation is wanted of some of the species 

 of Linnrciis, chosen from among those which present more or 

 less of varied forms. These species ought to be wild [s/ oitarias) 

 plants, to the number of ten at least, and of twenty or more, be- 

 longing to two natural families at least, and inhabiting well- 

 explored countries, such as Europe, the United States, &c. The 

 author ought to discover, describe, and classify all the forms 

 more or less distinct, and more or kss hereditary, which are 

 included in the Linnean species, being careful to intimate their 

 habitat, their station. lie ought to study their mode of fecun- 

 dation, and to judge how far certain forms may be attributed to 

 crossing. The class'fication of forms into species, races, varieties, 

 and other subdivisions as may be necessary, ought to be based at 

 once upon the external forms and on the more intimate affinities 

 demonstrated by fecundation and grafting. 



II. For competition in 1S76, for which the limit is fixed on 

 Jan. I, 1S76. 



1. Exact researches are asked for concerning the dissolving 

 power of water, and of water charged with carbonic acid, for 

 gypsum, chalk, and dolomite, at different temperatures and 

 pressures, and in the case of the simultaneous presence of marine 

 salt and other common soluble salts. 



2. The same is asked for silex and the most common natural 

 silicates. 



3. To suljmit to a new investigation the structure of the 

 kidneys of Mammalia, specially in reference to tlie epithelial 

 lining of the different parts of the renal tubes. 



4. A critical examination of recent researches from which it 

 would appear to result that the [leptones of different albumenoid 

 matters are mixtures of substances in part already known and 

 partly yet unknown. This critical examination should be com- 

 pleted by personal researches. 



5. To determine exactly in Weber units, the resistance of a 

 column of mercury of one metre in length and of one square 

 millimetre in section, at o\ 



6. To make better known, by careful experiments, the relation 

 between the two kinds of electrical units, electro-magnetic units 

 and electro-static units. 



7. New experiments tending to determine the influence of 

 pressure on chemical action. 



The prize offered by the Society for each of these questions 

 consists (at the choice of the competitors) either of a gold medal 

 bearing the ordinary stamp of the Society, along with the name 

 of the author and the date, or a sum of 150 florins. A supple- 

 mentary premium of 150 florins may, moreover, be awarded if 

 any memoir is deemed worthy of it. The memoirs sent for com- 

 petition ought to be written in one of the following languages : — 

 French, Dutch, English, Italian, Latin, or German {Itut not in 

 German character). They ought to be accompanied by a sealed 

 envelope containing the name of the author, who ought not to 

 make himself otherwise known. 



COMMON WILD FLOWERS CONSIDERED IN 



RELA TION TO INSECTS * 

 A T the close of the last century, Conrad Sprengel published a 

 ^*- most valuable work on Flowers, in which he pointed out 

 that their forms and colours, their scent, honey, and general 

 structure, have reference to the visits of insects, which are of 

 importance to Flowers in transferring the pollen from the stamens 

 to the pistil. .Sprengel's admirable work, however, did not 

 attract the attention it deserved, and remained comparatively 

 unknown until Mr. Darwin devoted himself to the subject. Our 

 illustrious countryman was tlie first to perceive that insecis are of 

 importance to Flowers, not only in tr.anslerring the pollen from 

 the stamens to the pistil, but in transferring it from the stamens 

 of one flower to the pistil of another. Sprengel had, indeed, 

 observed in more than one instance that this was the ca';e ; but 

 he did not appreciate the inqiortance of the fact. Mr. 

 Darwin's remarkable memoir on Primula, to wliich I shall 

 again have occasion to refer more th.an once, was published in 

 1S62 ; in this treatise the importance of cross-fertilisation, as it 

 may be called, was conclusively proved, and he has since illus- 

 trated the same rule by a number of researches on Orchids, 



* Address by Sir John Lubbock, Eart., F. R.S-, M the Belfast nieuting of 

 he British Association, August 1874. 



Linuni, Lythrum, and a variety of otlier plants. The new im- 

 pulse thus given to the study of Flowers has been followed up 

 in this country by Hooker, Ogle, Bennett, and other naturalists, 

 and on the Continent by Axell, Delpino, Hildebrand, and 

 especially by Dr. H. Miiller, who has published an excellent 

 work on the suViject, bringing together the observations of others 

 and adding to them an immense number of his own. 



Everyone knows how important flowers are to insects ; 

 everyone knows that bees, butterflies, &c., derive the main 

 part of their nourishment from the honey or pollen of flowers ; 

 but comparatively few are aware, on the other hand, how much 

 the flowers themselves are dependent on insects. 



Yet it is not too much to say, if flowers are very useful to 

 insects, insects, on the other hand, are in many cases absolutely 

 necessary to flowers ; that if insects have been in some respects 

 modified and adapted with a view to the acquirement of honey 

 and pollen ; flowers, on the other hand, owe their scent and 

 colours, nay, their very existence in the present form, to insecis. 

 Not only have the brilliant colours, the smell, and the honey ot 

 flowers been gradually developed under the action of natural 

 selection to encourage the visits of insects, but the very arrange- 

 ment of the colours, the circular bands and radiating lines,* the 

 form, size, and position of the petals, are arranged with reference 

 to the visits of insects, and in such a manner ,is to ensure the 

 grand object which renders these visits necessary. Thus the lines 

 and bands by which so many flowers are ornamented have refe- 

 rence to the position of the honey; and it may be obstrved that 

 these honey-guides are absent in night-flo\\'ers, where of course 

 they would not show, and would therefore be useless, as, for in- 

 stance, in Lyclniis -.■afcrtiiia, or Silciic inilaiis. Night-flowers, 

 moreover, ate generally pale ; for instance. Lychnis vcspa-t}na'\% 

 white, while I.vclutis i/iiinin which flowers by day is red. 



That the colour of the corolla has reference to the visits of in- 

 sects is well shown by the case of flowers, which — as, for in- 

 stance, the ray or outside fl .rets of Cfntaiiren n'a>nis — have neither 

 stamens nor pistils, and serve, therefore, exclusively to render the 

 flower-head more conspicuous. The calyx, moreover, is usually 

 green ; but when the position of the flower is such that it is 

 much exposed, it becomes brightly coloured, as, for instance, in 

 the Berberry. 



If it be objected to me that I am <7«?<;«!>/^ the existence of 

 these gradual modifications, I should reply that it is not here 

 my purpose to discuss the doctrine of Natural Selection, I may, 

 however, remind the reader that Mr. Darwin's theory is based 

 on the following considerations : — i. That no two animals or 

 plants in nature are identical in all respects. 2. That the oft"- 

 spring tend to inherit the peculiarities of their parents. 3. That 

 of those which come into existence only a certain number reach 

 maturity. 4. That those which are, on the whole, best adapted 

 to the circumstances in which they are placed, are most likely to 

 leave des<:endants. 



No one of these statements is, or can be, disputed, and they 

 seem fully to justify the conclusions which Mr. Darwin has de- 

 duced from them, though not all those which have been attri- 

 buted to him by his 0]iponents. 



Now, applying these considerations to flowers, if it is an ad- 

 vantage to them that they should be visited by insects (and that 

 this is so will presently be shown), then it is obvious that those 

 flowers which, either by their larger size, or brighter colour, or 

 sweeter scent, or greater richness in honey, are most attractive to 

 insects, will, ceUris paribus, have an advantage in the struggle 

 for existence, and be most likely to perpetuate their race. 



There are, indeed, other ways in which insects may be useful 

 to plants. Thus, a species of acacia mentioned by Mr. Bcll,t if 

 unprotected, is apt to be stripped of its leaves by a species of 

 leaf-cutting ant, which uses the leaves, not directly for food, but, 

 according to Mr. Belt, to grow mushrooms on. 



The acacia, however, bears hollow thorns, and each leaflet 

 produces honey in a crater-formed gland at the base, and a small, 

 sweet, pear-shaped body at the tip. In consequence it is in- 

 habited by myriads of a small ant, Psciidomyi ma Incolor, which 

 nests in the hollow thorns, and thus finds meat, drink, and lodg- 

 ing all provided for it. These ants are continually roaming over the 

 plant, and constitute a most efficient bodyguard, not only driv- 

 ing off the leaf-cutting ants, but even in Mr. Belt's opinion ren- 

 dering it less liable to be eaten by herbivorous mammalia. 



* I did not realise the impoi-tance of these guiding marks uiuil, by experi- 

 ments on bees, I saw what difficulty they experience if honey, which is put 

 out for them, is moved even slightly from its usual pl.ice. 



t F. Miiller has observed similar facts in,Sta. Catharina. (Nature, vol. x. 

 p. .02 ) 



