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Show 304 DARWINISM CJIAl'. Colours of Fruits. It is when we come to the essential parts of plants on which their perpetuation and distribution depends,_ thn.t we find colour larcroly utilised for a distinct purpose m flow ers and fruits. .In° the former we find attractive colour. ancl guiding marks to secure cross- fortilisatio~ by insects; i11 the latter attractive or protective colo:at10n,. tho first t.o attract birds or other animals when tho frmts arc mtondcd to lH' e::tton, the second to enable them to escape being eaten when it would be injurious to the species. ~he colour_ phcno~ c n a. of fruits boincr much the most simple w1ll be consHlcred fi ri'i l. The pcrp~tuation and therefore the vc~y cxi. tcnce_ of c:wh species of flowering plant depend upon 1ts seed. bm_n~ pn~scrvecl from destruction and more or less cffcctnally ch.-penw<l over a considerable area.. The di:pcrsal is eft'ected cit her mechanically or by the agency of animals. M cchanic:tl <1 ispersal is chiefly by means of air-currents, ~nd l~rgc nmnl1_<·rs of seeds are specially adapted to be so earned, mthcr l>y hc1ng clothed with down or pappus, as in the well-known thi.tlc a rHl dandelion seeds; by having wings or other appcn<~agcs, as in the sycamore, birch, and many other trees; by b01ng thrown to a considerable distance by the splitting of the sccd-vcsscl, and by many other curious dcvices.1 V cry large nnmhcrs of seeds, however, are so small and light that they can he en rrie<l enormous distances by gales of wind, more especially as most of this kind are flattened or curved, so as to expose :t large surface in proportion to their weight. Tho. c which nt·c carried by animals have their surfaces, or that of the scc<lvcsscl, armed with minute hooks, or some prickly coYcring which attaches itself to the hair of mammali:.t or the feat hen; of birds, as in the burdock, cleavers, and many other spc\'ics. Others again arc sticky, as in Plumbago curoprea, mistletoe, and many foreign plants. All the seeds or seed- vessels which arc a,daptcd to ho dispersed in any of these ways are of dull protocti vc tin~s, ~o that when they fn11 on the ground they arc almost lll<ltstinguishablc; besides which, they arc usually small, hard, and 1 For a popular sketch of th ese, see Sir J. Lull bock's Flowe1·s, Frnits, and Leav~ or any general uotanical work. XI THE SPECIAL OLOURS OF PLANTS 305 altogether un_attractive, never having ttny soft, juicy pulp; while the od1ble seeds often bear such a, small proportion to the hard, dry envelopes or appendages, that few animals would care to eat them. The Meaning of Nuts. There is, ~owev_er, anoth~r class of fruits or seeds, u. ually termed nuts, m wh10h there IS a large amount of edible matter often very ~greeable to the taste, and especially attractiv~ and nounshmg to a large number of a.nimals. But when eaten, the seed i~ des~royed and the existence of the species en~a.ngorcd. It 1s eVIdent, therefore, that it is by a ki ncl of ~cc1dent that these ~uts are eatable ; ancl that they arc not mtended to be oaten 1s shown by the special care nature seems to have taken to conceal or to protect them. \Y e sec that all our COJI_lm_on ~uts are green when on the tree, so as not easily to be d1stmgmshccl from the leaves; but when ripe they tnrn ~1ro~~' so ~hat when they bll on to the crrouncl they arc equally md1stmgmshablc among the dead leaves and twigs, or on the brow~ earth .. Then they arc ~lmost always protected by hard coven_ngs, as m hazcl_-nuts, whJCh are concealed by the enlarged leafy mvolucrc, and m the large tropical brazil-nuts and cocoanuts by such a hard and tough case as to lJo safe from almost every anima!. . Others have an external bitter rind, as in the walnut; while m tho chestnuts and beechnuts two or three fruits are enclosed in a prickly involucre. Notwithstanding a!l these _precautions, nuts a.rc largely devoured by mammaha and bn·ds; but as they are chiefly the product of trees or shrubs of considerable lon o·evity a_nd arc generally produced in gTeat profusion, the pe~petu~ tJon of the species is not endangered. In some cases the devourers of nuts may aid in their dispersal, as they probably now and then swallow ~he _seed wh_olc, or not sufficiently crushed to prevent germmat10n; while squirrels have been observed to bury nuts, many of which are forcrotten and afterwards grow in places they could not haveb otherwi e reached.I Nuts, especially the larger kinds which arc so ~ell protect~~ by their hard, nearly globular cases, have their . dispersal facihtatcd by rolling down hill, and more especially 1 Natu1·e, vol. xv. p. 117. X |
