66 



KNOWLEDGE 



[Nov. 25, 1881. 



ini;, the ovules in its carpels must necessarily be fertilised 

 liy polleiu Now, all the earlii\st (lowers consisted merely of 

 stamens and enqiels ; they hud no petals at all. But, as 

 Jlr. l)arwin has shown, Howits which are fertilised hy 

 pollen from a neighliourinf,' plant produce more seed and 

 healthier seedlings than those which are fertilised liy the 

 produce of their own stamens. Hence, any modification 

 which promoted such cross-fertilisation would lienefit the 

 plants in wliich it occurred l>y giving them an advantage 

 over tlieir rivals in the struggle for existence. Now, there 

 are two ways in which flowers have thus acquired special 

 adaptations for fertilising one another. Some of them have 

 developed hanging stamens which shake out their pollen to 

 the wind, and such flowers are also provided with feathery 

 collecting surfaces to the carpels, so as to catch the stray 

 grains which may happen to be wafted to them from their 

 neighbours by the breeze. Plants of this type ne\er 

 possess bright-coloured petals. A second class, on the 

 other hand, have learned to utilise the winged insects 

 which visit their Ijlossoms in search of food. These welcome 

 little pilferers, in passing from head to head, carry the 

 pollen of one plant to the carpels of another, and so assist 

 the flower in efJ'ecting the desired cross-fertilisation. This 

 class, to which the buttercup belongs, has usually developed 

 various inducements of food, scent, and colour, in order to 

 attract the fertilising insects. Those flowers which best 

 succeeded in alluring their little winged guests would 

 naturally hold their o\m against all less highly endowed 

 competitors, and would hand on their own constitution to 

 their descendants. In this way insect-fertilised plants 

 have acquired the bright petals and sweet scents which 

 chiefly make them noticeable to our human senses. A brief 

 examination of the buttercup blossom will show us the use 

 which they subserve, and the way in which they act in the 

 simplest forms of insect-fertilised flowers. 



Pull out one of the golden petals from the outside of 

 the head, and you will see at its l)ase a small hollow spot, 

 covered by a tiny concave scale. That spot is the nectary, 

 and it contains a single drop of pure honey. The honey is 

 put there to entice bees and other insects ; it is the wage 

 oflered them by the plant in return for the service which 

 they perform for it in fertilising its seeds. The golden hue 

 of the petals, again, acts as an advertisement for the honey ; 

 the Vices know that such bright hues are never found in 

 any flowers except those which specially lay themselves out 

 to bid for their favour. When a bee sees the brilliant 

 colour, he flies straight towards the blossom and settles 

 on the little boss of carpels in the centre. Here he 

 sips the honey for liis own behoof, and at the same time 

 dusts himself with pollen on behalf of the flower ; for, 

 as soon as the blossom opens, the stamens discharge 

 their precious burden, beginning from the outside 

 and slowly ripening towards the centre. At this 

 early stage, however, the carpels an; not yet mature 

 for impregnation, and so they avoid being fertilised from 

 the pollen of their own stamens. If the bee flies away to 

 another buttercup which happens to be still in the same 

 stage of development, he only collects more pollen about 

 his head and thighs ; but if he alights on a somewhat 

 older liuttercup, he finds its stamens withered and its car- 

 pels fully mature for impregnation. Some of the pollen is 

 then sure to fall on the sensitive surface of the carpels. 

 Thus, while he seeks honey for himself, he unconsciously 

 allbrds his host all the advantages of cross-fertilisation ; 

 and it is because he does so that the flower has been 

 enabled to develope its complicated arrangement of petals 

 and nectaries for his delectation. 



The buttercup, then, with its five separate simple petals, 

 its many stamens, and its central one-seeded carpels, maj- 



be regarded as a good example of the earliest type of 

 insect-fertilised flowers. In some other plants, such as the 

 harebell and the primrose, the separate petals have coalesced 

 into a single tubular corolla ; while in others, again, they 

 have assumed various fantastic shapes ; but all of them are 

 ultimately derived from flowers like the butt<-rcup, which 

 thus contains in itself all the essential elements of a perfect 

 insect-fertilised plant 



SOLIDS, LIQUIDS, AND GASES. 



By W. M.^ttied Williams. 

 PART II. 



MULTITUDES of examples may be cited illustrating 

 the viscosity of bodies that we usually regard as 

 types of solidity, such, for example, as the rocks forming 

 the earth's crust In the " Black Country " of South 

 Staffordshire, which is undermined by the gi'eat ten-yard 

 coal-seam, cottages, chimney-shafts, and other buildings 

 may be seen leaning over most grotesquely, houses spUt 

 down the middle by the subsidence or inclination of one 

 side, great hollows in fields or across roads that were once 

 flat, and a variety of other distortions, due to the sinking 

 of the gradual rock-strata that have been undermined by 

 the colliery workings. In some cases the rocks are split, 

 l)ut usually the subsidence is a gradual bending or flowing 

 do-wn of the rocks to fill up the vacuity, as water tills a 

 hollow or " finds its own level." 



I have seen many cases of the downward curvature of 

 the roof of a coal-pit, and have been told that in some 

 cases the sun'ounding pressure causes the floor to curs'e 

 upwards, but have not seen this. 



As KxowLEDGE will doubtless have many readers in the 

 colliery districts, some of them may be able to supply 

 reliable evidence of this, accompanied with careful measure- 

 ment of the amount of upward curvature or upheaving in a 

 stated breadth of road or working. 



Earthquakes afford another example. Tlie so-called 

 solid crust of the earth is upheaved and cast into positive 

 billows that wave away on all sides from the centre of dis- 

 turbance. The earth-billows of the great Lisbon earth- 

 quake of 1753 travelled to this country, and when they 

 reached Loch Lomond, were still of sufficient magnitude to 

 raise and lower its banks through a perpendicular i-ange 

 of two feet four inches. 



It is quite possible, or, I may say, probable, that there 

 are tides of the earth as well as of the waters, and the 

 subject has occupied much attention and raised some dis- 

 cussion among mathematicians. If the earth has a fluid 

 centre, and only a comparatively thin crust, as some 

 suppose, there must be such tides, produced by the gravi- 

 tation of the moon and the sun. 



Ice presents some interesting results of this viscosity. 

 At a certain height, varying with latitude, aspect, Arc, we 

 reach " the snow line " of mountain slopes, above which the 

 snow of winter remains unnielted during summer, and, in 

 most cases, goes on accumulating. It soon loses its floc- 

 culent, flakey character, and becomes coherent, clear blue 

 ice by the pressure of its o^^•n weight 



A rather complex theory has been propounded to explain 

 this change — the theory of regeJation — i.e., refreezing, a 

 theory which assumes that the pressure between the sur- 

 faces first thaws a film of ice at the surfaces of contact, 

 and that presently this refreezes, and thus efiects a heating 

 or general solidification. Faraday found that two pieces 

 of ice wnXh moistened surfaces united if pressed together 



