Dog's mercury is one of the oddest English flowers I know. Each blossom has three small green petals6, and either several stamens, or else a pistil, in the centre. There is nothing particularly remarkable7 in the flower being green, for thousands of other flowers are green and we never notice them as in any way unusual. In fact, we never as a rule notice green blossoms at all. Yet anybody who picked a piece of dog's mercury could not fail to be struck by its curious appearance. It does not in the least resemble the inconspicuous green flowers of the stinging-nettle, or of most forest trees: it has a very distinct set of petals which at once impress one with the idea that they ought to be coloured. And so indeed they ought: for dog's mercury is a degenerate9 plant which once possessed10 a brilliant corolla and was fertilised by insects, but which has now fallen from its high estate and reverted12 to the less advanced mode of fertilisation by the intermediation of the wind. For some unknown reason or other this species and all its relations have discovered that they get on better by the latter and usually more wasteful13 plan than by the former and usually more economical one. Hence they have given up producing large bright petals, because they no longer need to attract the eyes of insects; and they have also given up the manufacture of honey, which under their new circumstances would be a mere14 waste of substance to them. But the dog's mercury still retains a distinct mark of its earlier insect-attracting habits in these three diminutive15 petals. Others of its relations have lost even these, so that the original floral form is almost completely obscured in their case. The spurges are familiar English roadside examples, and their flowers are so completely degraded that even botanists16 for a long time mistook their nature and analogies.
The male and female flowers of dog's mercury have taken to living upon separate plants. Why is this? Well, there was no doubt a time when every blossom had both stamens and pistil, as dog-roses and buttercups always have. But when the plant took to wind fertilisation it underwent a change of structure. The stamens on some blossoms became aborted17, while the pistil became aborted on others. This was necessary in order to prevent self-fertilisation; for otherwise the pollen18 of each blossom, hanging out as it does to the wind, would have been very liable to fall upon its own pistil. But the present arrangement obviates19 any such contingency20, by making one plant bear all the male flowers and another plant all the female ones. Why, again, are the petals green? I think because dog's mercury would be positively21 injured by the visits of insects. It has no honey to offer them, and if they came to it at all, they would only eat up the pollen itself. Hence I suspect that those flowers among the mercuries which showed any tendency to retain the original coloured petals would soon get weeded out, because insects would eat up all their pollen, thus preventing them from fertilising others; while those which had green petals would never be noticed and so would be permitted to fertilise one another after their new fashion. In fact, when a blossom which has once depended upon insects for its fertilisation is driven by circumstances to depend upon the wind, it seems to derive22 a positive advantage from losing all those attractive features by which its ancestors formerly23 allured24 the eyes of bees or beetles25.
Here, again, on the roadside is a bit of plantain. Everybody knows its flat rosette of green leaves and its tall spike26 of grass-like blossom, with long stamens hanging out to catch the breeze. Now plantain is a case exactly analogous27 to dog's mercury. It is an example of a degraded blossom. Once upon a time it was a sort of distant cousin to the veronica, that pretty sky-blue speedwell which abounds28 among the meadows in June and July. But these particular speedwells gave up devoting themselves to insects and became adapted for fertilisation by the wind instead. So you must look close at them to see at all that the flowering spike is made up of a hundred separate little four-rayed blossoms, whose pale and faded petals are tucked away out of sight flat against the stem. Yet their shape and arrangement distinctly recall the beautiful veronica, and leave one in little doubt as to the origin of the plant. At the same time a curious device has sprung up which answers just the same purpose as the separation of the male and female flowers on the dog's mercury. Each plantain blossom has both stamens and pistils, but the pistils come to maturity29 first, and are fertilised by pollen blown to them from some neighbouring spike. Their feathery plumes30 are admirably adapted for catching31 and utilising any stray golden grain which happens to pass that way. After the pistils have faded, the stamens ripen32, and hang out at the end of long waving filaments33, so as to discharge all their pollen with effect. On each spike of blossoms the lower flowerets open first; and so, if you pick a half-blown spike, you will see that all the stamens are ripe below, and all the pistils above. Were the opposite arrangement to occur, the pollen would fall from the stamens to the lower flowers of the same stalk; but as the pistils below have always been fertilised and withered34 before the stamens ripen, there is no chance of any such accident and its consequent evil results. Thus one can see clearly that the plantain has become wholly adapted to wind-fertilisation, and as a natural effect has all but lost its bright-coloured corolla.
Common groundsel is also a case of the same kind; but here the degradation35 has not gone nearly so far. I venture to conjecture36, therefore, that groundsel has been embarked37 for a shorter time upon its downward course. For evolution is not, as most people seem to fancy, a thing which used once to take place; it is a process taking place around us every day, and it must necessarily continue to take place to the end of all time. By family the groundsel is a daisy; but it has acquired the strange and somewhat abnormal habit of self-fertilisation, which in all probability will ultimately lead to its total extinction38. Hence it does not need the assistance of insects; and it has accordingly never developed or else got rid of the bright outer ray-florets which may once have attracted them. Its tiny bell-shaped blossoms still retain their dwarf39 yellow corollas; but they are almost hidden by the green cup-like investment of the flower-head, and they are not conspicuous8 enough to arrest the attention of the passing flies. Here, then, we have an example of a plant just beginning to start on the retrograde path already traversed by the plantain and the spurges. If we could meet prophetically with a groundsel of some remote future century, I have little doubt we should find its bell-shaped petals as completely degraded as those of the plantain in our own day.
The general principle which these cases illustrate40 is that when flowers have always been fertilised by the wind, they never have brilliant corollas; when they acquire the habit of impregnating their kind by the intervention41 of insects, they almost always acquire at the same time alluring42 colours, perfumes, and honey; and when they have once been so impregnated, and then revert11 once more to wind-fertilisation, or become self-fertilisers, they generally retain some symptoms of their earlier habits, in the presence of dwarfed43 and useless petals, sometimes green, or if not green at least devoid44 of their former attractive colouring. Thus every plant bears upon its very face the history of its whole previous development.
点击收听单词发音
1 tangled | |
adj. 纠缠的,紊乱的 动词tangle的过去式和过去分词 | |
参考例句: |
|
|
2 chestnut | |
n.栗树,栗子 | |
参考例句: |
|
|
3 perennial | |
adj.终年的;长久的 | |
参考例句: |
|
|
4 virtue | |
n.德行,美德;贞操;优点;功效,效力 | |
参考例句: |
|
|
5 practitioners | |
n.习艺者,实习者( practitioner的名词复数 );从业者(尤指医师) | |
参考例句: |
|
|
6 petals | |
n.花瓣( petal的名词复数 ) | |
参考例句: |
|
|
7 remarkable | |
adj.显著的,异常的,非凡的,值得注意的 | |
参考例句: |
|
|
8 conspicuous | |
adj.明眼的,惹人注目的;炫耀的,摆阔气的 | |
参考例句: |
|
|
9 degenerate | |
v.退步,堕落;adj.退步的,堕落的;n.堕落者 | |
参考例句: |
|
|
10 possessed | |
adj.疯狂的;拥有的,占有的 | |
参考例句: |
|
|
11 revert | |
v.恢复,复归,回到 | |
参考例句: |
|
|
12 reverted | |
恢复( revert的过去式和过去分词 ); 重提; 回到…上; 归还 | |
参考例句: |
|
|
13 wasteful | |
adj.(造成)浪费的,挥霍的 | |
参考例句: |
|
|
14 mere | |
adj.纯粹的;仅仅,只不过 | |
参考例句: |
|
|
15 diminutive | |
adj.小巧可爱的,小的 | |
参考例句: |
|
|
16 botanists | |
n.植物学家,研究植物的人( botanist的名词复数 ) | |
参考例句: |
|
|
17 aborted | |
adj.流产的,失败的v.(使)流产( abort的过去式和过去分词 );(使)(某事物)中止;(因故障等而)(使)(飞机、宇宙飞船、导弹等)中断飞行;(使)(飞行任务等)中途失败 | |
参考例句: |
|
|
18 pollen | |
n.[植]花粉 | |
参考例句: |
|
|
19 obviates | |
v.避免,消除(贫困、不方便等)( obviate的第三人称单数 ) | |
参考例句: |
|
|
20 contingency | |
n.意外事件,可能性 | |
参考例句: |
|
|
21 positively | |
adv.明确地,断然,坚决地;实在,确实 | |
参考例句: |
|
|
22 derive | |
v.取得;导出;引申;来自;源自;出自 | |
参考例句: |
|
|
23 formerly | |
adv.从前,以前 | |
参考例句: |
|
|
24 allured | |
诱引,吸引( allure的过去式和过去分词 ) | |
参考例句: |
|
|
25 beetles | |
n.甲虫( beetle的名词复数 ) | |
参考例句: |
|
|
26 spike | |
n.长钉,钉鞋;v.以大钉钉牢,使...失效 | |
参考例句: |
|
|
27 analogous | |
adj.相似的;类似的 | |
参考例句: |
|
|
28 abounds | |
v.大量存在,充满,富于( abound的第三人称单数 ) | |
参考例句: |
|
|
29 maturity | |
n.成熟;完成;(支票、债券等)到期 | |
参考例句: |
|
|
30 plumes | |
羽毛( plume的名词复数 ); 羽毛饰; 羽毛状物; 升上空中的羽状物 | |
参考例句: |
|
|
31 catching | |
adj.易传染的,有魅力的,迷人的,接住 | |
参考例句: |
|
|
32 ripen | |
vt.使成熟;vi.成熟 | |
参考例句: |
|
|
33 filaments | |
n.(电灯泡的)灯丝( filament的名词复数 );丝极;细丝;丝状物 | |
参考例句: |
|
|
34 withered | |
adj. 枯萎的,干瘪的,(人身体的部分器官)因病萎缩的或未发育良好的 动词wither的过去式和过去分词形式 | |
参考例句: |
|
|
35 degradation | |
n.降级;低落;退化;陵削;降解;衰变 | |
参考例句: |
|
|
36 conjecture | |
n./v.推测,猜测 | |
参考例句: |
|
|
37 embarked | |
乘船( embark的过去式和过去分词 ); 装载; 从事 | |
参考例句: |
|
|
38 extinction | |
n.熄灭,消亡,消灭,灭绝,绝种 | |
参考例句: |
|
|
39 dwarf | |
n.矮子,侏儒,矮小的动植物;vt.使…矮小 | |
参考例句: |
|
|
40 illustrate | |
v.举例说明,阐明;图解,加插图 | |
参考例句: |
|
|
41 intervention | |
n.介入,干涉,干预 | |
参考例句: |
|
|
42 alluring | |
adj.吸引人的,迷人的 | |
参考例句: |
|
|
43 dwarfed | |
vt.(使)显得矮小(dwarf的过去式与过去分词形式) | |
参考例句: |
|
|
44 devoid | |
adj.全无的,缺乏的 | |
参考例句: |
|
|
欢迎访问英文小说网 |