♦ KNOWLEDGE ♦ 



[Nov. 1, 1885 



stern logic of their own particular and immovable 

 environment. 



As a matter of fact, many of the smaller and simpler 

 annuals do merely drop their seeds just beneath the 

 parent plant, and don't suffer much in the long run from 

 the resulting consequences. Some of them are so small, 

 and their roots spread such a very little way in the earth, 

 that the seed can hardlj' drop out of the capsule without 

 finding a decently-fit po.sition in life. Others grow upon 

 banks or slopes, where the mere lie of the ground enables 

 them to get a fresh foothold — a condition very well 

 exemplified in plants like the wallflower and the ordinary 

 weeds of our cliffs and precipices. In such cases, the 

 chapter of accidents alone suffices to carry away a suffi- 

 cient number of seeds for the due dispersion and survival 

 of the species. Mr. A. R. Wallace has well noted, how- 

 ever, that in instances of this sort the seeds are usually 

 small and relatively numerous ; a grent many super- 

 numer.xry youug are produced, out of all which only one 

 or two on an average arrive at maturity. Compare this 

 with the parallel instance of fish among the vertebrates, 

 where sometimes, as with the cod, no less than three 

 million eggs are spawned annually by each femxle, for 

 the final average production of a single pair of adult 

 codfish. 



The first advance from this simplest mode of dropping 

 seeds to take their chance upon the ground beneath is 

 seen in a few plants like our common mouse- 5 ir chick- 

 weed, which has the capsule cocked up a little at the 

 end, and opening with small teeth, so as to prevent the 

 seeds from falling out except during a rather high wind. 

 The wind then jerks them out forcibly, and necessarily 

 carries them to some slight distance from the mother- 

 plant. I have very little doubt that almost all the cap- 

 sules which open at the top only with distinct teeth 

 have been developed for this very purpose, and that they 

 mark an incipient advance from the lower and weedier 

 to the higher and more dominant members of their 

 respective families. For example, in this very same 

 chickweed family, our common chickweed, a plant often 

 self-fertilised, and extremely low in type, has capsules 

 which generally open to the very base, allowing the seeds 

 merely to drop out, hap-hazard, anyhow ; while on the 

 other hand the large, handsome, and highly-developed 

 red campion, with its elaborate arrangements for insect, 

 fertilisation, and its division of the sexes on distinct 

 plants, has also a capsule shaped something like an ordi- 

 nary water-bottle, narrowed at the top, and opening in 

 ten short teeth, so that the seeds can only be shaken out 

 by a high wind, which, of course, carries them away to 

 a considerable distance. The same sort of progressive 

 advance can be traced in many families, from the very 

 simplest to the highest forms. 



The yellow-rattle, which grows aa a common parasite 

 on the roots of grasses in English meadows affords us an 

 admirable transitional type between these merely casual 

 wind-dispersed seeds and those in which the most 

 advanced devices for wind-dispersion have become fixed 

 and settled by natural selection. Its big inflated capsules 

 are filled with light and flattened seeds, which shake 

 noisily in a gentle breeze, and so have gained for the 

 plant its vernacular name from village children. Some- 

 times these seeds are distinctly winged, but sometimes 

 they are only flat and thin. In either case, the wind 

 shakes them at last out of the papery capsule, and carries 

 them along a couple of yards or so from their original 

 position before letting them drop upon the soil beneath. 

 Devices like these lead up insensibly to more developed 

 plans, such as that of the maple-tree, where the entire 



fruit, with the seed inside it, is borne on the breeze by a 

 large expanded membranous wing, so placed that it 

 rotates slowly like a parachute as it falls through 

 the air, and thus almost certainly ensures the wind 

 catching it before it finally alights fi-om its aerial 

 voyage. Every amateur gardener must have observed 

 how very effectual is this means of dispersion 

 possessed by the maple tribe ; for young sycamore trees 

 are among the very commonest and mrst persistent 

 weeds in suburban gardens, even though there may not 

 be an adult sycamore anywhere in sight within a quarter 

 of a mile of the spot where the hardy seedlings are found 

 rooting themselves. Much the same sort of plan is also 

 pursued by the elm, the ash, the pine, and the linden ; 

 indeed, the necessity for remote dispersion is, of course, 

 far more obvious in the case of large trees than of any 

 other group of plants, both because such giants of the 

 vegetable world need more space for their roots to grow 

 in, and because the branches of the mother tree more 

 completely overshadow, stunt, and starve the struggling 

 seedlings than in the instance of any smaller and less 

 spreading species. 



Still more advanced is the method of dispersion by 

 feathery hairs, such as those of the wild English clematis, 

 the seed of the willow, and the ripe carpels of the pasque- 

 flower anemone. In the red valerian of our cottage- 

 gardens, now self-sown on many west-country cliffs, the 

 calyx slowly unrolls, after flowering, into a feathery 

 crown, which caps the fruit, and enables it to be lightly 

 borne about in every direction by the autumn breezes. 

 The thistles, doudelions, and n\any other plants of the 

 comjiosite family cai'ry the same provision yet a step 

 further, for here the otherwise functionless calyx has 

 assumed a new iise as a kite or parachute, and forms the 

 familiar down which enables the tiny seed-like fruits to 

 float freely through the surrounding air. It is curious 

 to note, however, that some low-growing composites, such 

 as the daisy, assuming a thoroughly weedy habit, and 

 supplied with vast quantities of sejiarate fruits, have 

 found it suit them better to dispense with this special 

 means of aerial dispersion, and seem to trust, like 

 many other degenerate plants, entirely to accident for 

 dissemination. 



Animals play so large a part in the fertilisation of 

 flowers that we might naturally expect to find them 

 filling a considerable place also in the dispersion of seeds. 

 And this expectation is fully realised, for an immense 

 number of plants owe their dissemination almost entirely 

 to the good services of birds or mammals, in some cases 

 voluntarily rendered, and in other cases involuntarily. 

 That fruits and berries are so dispersed has long been a 

 familiar fact to naturalists. The bright colour of the 

 pulpy exterior attracts the bii-ds, just as the petals of 

 flowers attract bees and butterflies. The sugary juices 

 and pleasant flavours answer exactly to the honey and 

 perfume. These things cause the fruit as a whole to be 

 eagerly sought and greedily devoured. On the other 

 hand, the actual seed itself is usually enclosed in a hard 

 and iiuligestible stony covering, or is otherwise protected 

 from the beaks and gizzards of its treacherous friends. 

 In this manner, the sloes, haws, strawberries, and black- 

 berries are reproduced from generation to generation by 

 the kindly offices of our native birds. 



The devices for making animals involuntarily act the 

 part of seed-sowers to the enterjjrising plant, are no less 

 marked and interesting in their own way. Cleavers or 

 goose-grass, the " run-the-hedge " of country children, 

 has its twin fruit covered with an immense number of 

 tiny hooked prickles, which get entangled in the wool of 



