登陆注册
15713900000038

第38章

On the belief that this is a law of nature, we can, I think, understand several large classes of facts, such as the following, which on any other view are inexplicable. Every hybridizer knows how unfavourable exposure to wet is to the fertilisation of a flower, yet what a multitude of flowers have their anthers and stigmas fully exposed to the weather! but if an occasional cross be indispensable, the fullest freedom for the entrance of pollen from another individual will explain this state of exposure, more especially as the plant's own anthers and pistil generally stand so close together that self-fertilisation seems almost inevitable. Many flowers, on the other hand, have their organs of fructification closely enclosed, as in the great papilionaceous or pea-family; but in several, perhaps in all, such flowers, there is a very curious adaptation between the structure of the flower and the manner in which bees suck the nectar; for, in doing this, they either push the flower's own pollen on the stigma, or bring pollen from another flower. So necessary are the visits of bees to papilionaceous flowers, that I have found, by experiments published elsewhere, that their fertility is greatly diminished if these visits be prevented. Now, it is scarcely possible that bees should fly from flower to flower, and not carry pollen from one to the other, to the great good, as I believe, of the plant.

Bees will act like a camel-hair pencil, and it is quite sufficient just to touch the anthers of one flower and then the stigma of another with the same brush to ensure fertilisation; but it must not be supposed that bees would thus produce a multitude of hybrids between distinct species;for if you bring on the same brush a plant's own pollen and pollen from another species, the former will have such a prepotent effect, that it will invariably and completely destroy, as has been shown by Gärtner, any influence from the foreign pollen.

When the stamens of a flower suddenly spring towards the pistil, or slowly move one after the other towards it, the contrivance seems adapted solely to ensure self-fertilisation; and no doubt it is useful for this end: but, the agency of insects is often required to cause the stamens to spring forward, as Kölreuter has shown to be the case with the barberry; and curiously in this very genus, which seems to have a special contrivance for self-fertilisation, it is well known that if very closely-allied forms or varieties are planted near each other, it is hardly possible to raise pure seedlings, so largely do they naturally cross. In many other cases, far from there being any aids for self-fertilisation, there are special contrivances, as I could show from the writings of C. C. Sprengel and from my own observations, which effectually prevent the stigma receiving pollen from its own flower: for instance, in Lobelia fulgens, there is a really beautiful and elaborate contrivance by which every one of the infinitely numerous pollen-granules are swept out of the conjoined anthers of each flower, before the stigma of that individual flower is ready to receive them; and as this flower is never visited, at least in my garden, by insects, it never sets a seed, though by placing pollen from one flower on the stigma of another, I raised plenty of seedlings; and whilst another species of Lobelia growing close by, which is visited by bees, seeds freely.

In very many other cases, though there be no special mechanical contrivance to prevent the stigma of a flower receiving its own pollen, yet, as C.

C. Sprengel has shown, and as I can confirm, either the anthers burst before the stigma is ready for fertilisation, or the stigma is ready before the pollen of that flower is ready, so that these plants have in fact separated sexes, and must habitually be crossed. How strange are these facts! How strange that the pollen and stigmatic surface of the same flower, though placed so close together, as if for the very purpose of self-fertilisation, should in so many cases be mutually useless to each other! How simply are these facts explained on the view of an occasional cross with a distinct individual being advantageous or indispensable!

If several varieties of the cabbage, radish, onion, and of some other plants, be allowed to seed near each other, a large majority, as I have found, of the seedlings thus raised will turn out mongrels: for instance, I raised 233 seedling cabbages from some plants of different varieties growing near each other, and of these only 78 were true to their kind, and some even of these were not perfectly true. Yet the pistil of each cabbage-flower is surrounded not only by its own six stamens, but by those of the many other flowers on the same plant. How, then, comes it that such a vast number of the seedlings are mongrelised? I suspect that it must arise from the pollen of a distinct variety having a prepotent effect over a flower's own pollen; and that this is part of the general law of good being derived from the intercrossing of distinct individuals of the same species. When distinct species are crossed the case is directly the reverse, for a plant's own pollen is always prepotent over foreign pollen; but to this subject we shall return in a future chapter.

同类推荐
热门推荐
  • 蓝眼睛玛丽

    蓝眼睛玛丽

    我是一座叫作“蓝眼睛玛丽”的岛。岛上的居民都是天赋异禀的拉锯战高手和从不纳税的刁民。这座岛的未来继承人一个是腹黑总裁,另一个是呆萌穷酸女。而目前管理岛上大小事务的人是一个讨人厌的强硬老妇人。身为一座岛,我无时无刻不为自己的未来担忧。
  • 四叶草之一世相约

    四叶草之一世相约

    tfboys在舞台上,他们是王。深陷爱情,她们和普通人一样只是个爱情白痴而已。颜璃沫:王俊凯我不爱你,却可以把你当成哥哥;易烊千玺你是我第一次遇见就令我怦然心动的人,可是我却配不上你;叶宇澈你很好,不用为我改变什么,因为我是一个骗子,我从来就没有想过要嫁给你。
  • 霸道老公逃不掉的爱

    霸道老公逃不掉的爱

    她自小被他父母收养,精明古怪很讨人爱。他从小冷漠无情,难以亲近。可是她的到来改变了他,他不顾一切得爱上了她,发誓非她不娶。可小丫头偏偏不领情,一度投进别人的怀抱,真让他不知所措,要怎麽抓住这丫头的心?
  • 厄运滔天

    厄运滔天

    天道崩残,万族失灵根;各为生存,倾轧加剧;谁能挽救毁灭中的世界
  • 幸福在夹缝中拐了一个弯

    幸福在夹缝中拐了一个弯

    他是农民的孩子,他无法选择自己的出生。因为家里贫穷,他主动选择了退学。在这二十世纪末,二十一世纪初,中国改革开放的黄金时代。古田选择留守乡村,用他青春的激情和梦想,在农村的夹缝中寻找着幸福。
  • 邪王的逆天宠妃

    邪王的逆天宠妃

    极品特工穿越萧家废柴四小姐,一个小庶女也敢骑在本小姐头上?风起云涌,看“废柴”如何逆天!
  • 如同末日

    如同末日

    如果全世界乃至整个银河,都发生了变化,人类,曾经的霸主,现在被拖下了舞台,各种生物咆哮,弱小而又蕴含强大力量的躯体,人类是否还可以从返巅峰
  • 火影校园

    火影校园

    主角凌若希在梦中见到他的死鬼表哥叶枫传给他超越现实的力量,于是主角就这样走上了颠覆世界变革的道路.。
  • 一千年以后,天气晴

    一千年以后,天气晴

    一千年以前,在那个终年落雪的虚空之境,他温暖的手第一次碰触了她。他给她取名,叫做——云之初。于是,云之初爱上了他。一千年以后,在这春光明媚的21世纪,他在所有人面前抓住了她的手。“她叫Fiarona。” 许年恩笑笑。那笑容,仿佛千年之前的一样。他伸手去握住她的,那温柔,亦同千年前他的抚摸。她忽然感觉到自己心里猛然软下去了一块,呆呆地望着那完美的侧脸,发不出声。如同,曾经作为式神那样,依然安静地站在他的身边。可是这一次,Fiarona再不敢爱上他。【情节虚构,请勿模仿】
  • 九阳邪神

    九阳邪神

    九阳神功铸就无上武道!一代邪神叶轻尘因为一件天地至宝而遭挚爱背叛,身死道消,灵魂却意外重生回到十六岁少年时期。前世,他是一个快意恩仇的邪神!今世,他立誓要做一个人见人怕的冷血杀神,人挡杀人,神挡杀神,杀尽诸天神佛!