March, igo6 ] 



KNOWLEDGE & SCIENTIFIC NEWS. 



375 



definitely origined, though Krypton seems to hold out 

 the most promise. 



Another theory ad\anced to explain the cause of aurorae 

 is the pressure of light repelling some of the corpuscular 

 matter surrounding the sun until it reaches the earth's 

 atmosphere, the electronsbeing directed into the magnetic 

 Meridian by the influence of the earth's magnetic field. 



Whate\cr he the cause and nnturf of the aurora, 

 there appears little doubt tliat auroral displays are very 

 frequently accompanied by magnetic disturbances, 

 though the converse does not hold. 



CORRESPONDENCE. 



The Evolution of the Flower. 



To the Editors of "Knowledge & Scientific News." 



Sirs, — There are a few rather important oversights in Mr 

 S. L. Bastin's paper on the above very interesting subject, 

 which I venture to suggest might be mentioned, as well as a 

 few additions made ; for since the paper is evidently intended 

 for beginners in Botany, a few extra remarks might supply an 

 additional interest to the subject. 



Comparing the use of flowers with vegetative methods of 

 propagation, the latter is often much more important than the 

 reader might, perhaps, suppose. Of course, annuals depend 

 entirely upon seed ; but perennials often multiply for far 

 longer periods than might be inferred from the expres- 

 sion, " for a time at any rate." This may be enlarged to 

 upwards of a century — c.i;., with Oxnlix CL-ynna, introduced into 

 Malta from the Cape before 1S04; for it has spread, and is 

 still doing so, by means of bulbs, along both north and south 

 shores of the Mediterranean Sea, but never sets seed at all 

 throughout that region. Our pilewort, too, rarely seeds. 



The object of Mr. Bastin's paper is to show that the four 

 organs of a flower — the sepals, petals, stamens, and carpels — 

 are fundamentally "homologous" with leaves; I'.i-., they might 

 have grown out into true leaves had they not appeared as 

 these organs. A little modification is here required; for it is 

 rare to find the sepals, for instance, as representing a !.■/«)/,■ 

 leaf or stalls and blade together. It usually corresponds with 

 the stall< or " petiole " only, as may be readily seen in a rose. 

 Very occasionally is a sepal the same thing as the blade, as in 

 the corn-cockle. 



Similarly, petals usually correspond only to the " filament " 

 of the stamens, so well described by Mr. Bastin in the Water- 

 lily or in Canna; but in the l^anunculus family it is the 

 " anther " of the stamen which is converted into the petal. 

 The student should compare the " nectaries " of R. aiiricomus, 

 R. F ii iiri It, a.ud other species, and he will soon discover /raiisi- 

 tioiml forms, showing that while one half, the outer, of the 

 anther grows into the broad yellow petal, the other, or inner 

 half, remains arrested, like a tiny flap ; in the spot between the 

 two, corresponding to the bottom of the anther-cells, honey is 

 secreted. 



The little honey-pots of Hellebores and Winter Aconite are 

 similarly constructed out of anthers. 



The " spurred " petals of the Columbine afford another good 

 illustration; while in "double" Columbines the numerous 

 " spurs " of the converted anthers fit into one another in radial 

 rows. 



In the " green rose " and Alpine Strawberry every part of 

 the flower is represented by a small green leaf; .some of them 

 may still carry an anther-cell showing, as Mr. Bastin explains, 

 their true homology. 



The first stage, therefore, was the conversion of leaves or 

 " leaf-sc;des"into carpels and stamens. This stage is seen in 

 the mull- flowers of Juniper and Cypress, though, unfortunately. 

 we have no good case of a " Gymnospcrm " passing into an 

 Angiosperm, the former having no indisputable representation 

 of a " carpellary leaf" at all. 



The second stage was to construct petals out of stamens, as 

 stated. 



In all the above plants mentioned the organs are 

 "free," 'but "cohesion" often stepped in and united the 

 parts of the " whorls " together. Mr. Bastin alludes to Cam- 

 panulas in illustration, but here the five united petals make 

 the bell, while the five sepals are external to it, and more or 

 less joined together, but not to the petals to form the bell (which 

 has only five free tips) as suggested by Mr. I^astin. Indeed, 

 in a garden variety called the " Cup and .Saucer," it is the broad, 

 flattened out blue calyx which makes the saucer, while the 

 corolla is the cup within it. 



It sometimes happens that the sepals of flowers are white or 

 coloured, as Mr. Bastin observes. Then they look tike petals, 

 and are called "petaloid." Such is the case with several 

 members of the Ranunculus family, as Clematis, Anemone, 

 Callui, Aconitum, and Delphinium, but tliey must not be con- 

 founded with petals. 



When such flowers become " double," it is not the sepals 

 which multiply, but the petals, together with the stamens and 

 carpels, which latter are now represented by petals, of which 

 the whole number may be upwards of fifty, as in a stock, and 

 many more in a garden Ranunculus. 



In Monocotyledons, such as tulips and hyacinths, the sepals 

 and petals had belter not be described as " identical," except 

 as to colour and form. 



Botanists regard them as being (;i"o distinct whorls, the outer 

 and the inner, at least when the parts are not united as in a 

 tulip, but they may be united as in the garden hyacinth. 

 Nevertheless they should be regarded really as 3 + 3 rather 

 than 6 in one whorl. 



Bracts, too, are rudimentary forms of leaves, being either 

 homologous with petioles only, as in Hellebores (H. firtidus is 

 an excellent illustration of a perfect transition in the reduction 

 and loss of blade, with a diminution of the petiole into a bract) 

 or of the blade only, as in Buttercups. 



Sometimes the bracts are brightly coloured and may puzzle 

 beginners. But they are always outside the flowers, often includ- 

 ing StivrK/y/mn-rs. as in Euphorbias and three in Boiigainvillea, a 

 proof that they are not really parts of a flower. 



They not infrequently mimic a flower. Thus species of 

 Cornus has four large white bracts, numerous minute flowers 

 being within them. It thus looks like the flower of a Clematis, 

 which may have four white sepals. A species of Euphorbia 

 has fi\e rounded scarlet "glands," exactlj' imitating a five- 

 petalled flower! 



It is only by a careful examination, which the beginner should 

 always make, before the imitation is detected. 



All these coloured organs, as Mr. Bastin rightly observes, 

 are to attract insects for pollenation. Nature sometimes .goes 

 so far as to put all her energy, so to say, into the corolla, as 

 to even sacrifice the stamens and pistils. Such is the case with 

 the outermost flowers of a truss of Hydnin^^ea, which has only 

 a coloured calyx, and the Guelder-rose, which has only a 

 corolla. Such, too, is the case with the large trumpet-shaped 

 " ray " florets on the head of a Centaurea. The outermost 

 flowers of these plants have sacrificed their power of setting 

 seed for the benefit of the commuuitv, consisting of incon- 

 spicuous but fertile flowers in their midst. 



.•\s sepals, petals, stamens .and carpels will sometimes 

 " revert " to be represented by true leaves, so may bracts. It 

 is not uncommonly so with plantains. Ivach of the umuerous, 

 minute flowers which form the dense spike, stand in the 

 "axil" of an extremely minute bract. Sometimes, however, 

 these bracts become "foliaceoiis " and grow out into small 

 leaves. 



In the "Green Dahlia," the usually colourless bracts or 

 scales, hidden among the flowers, become large, thick and green, 

 all the florets being totally arrested. This change is expressed 

 as the result of the " law of compensation," when one organ is 

 enlarged at the expense of another ; but why these changes 

 (ake place is a problem which cannot always be solved ; but 

 the lesson we learn from .all this is, the wonderful power 

 Nature possesses of constructing any organ she pleases out of 

 any other. It is not only in flowers, but a .general capability, 

 and is most admirably seen in such curious adaptations as the 

 means of climbing and of catching and devouring animal 

 prey, &c. 



George Hensi.ow. 



