Experiments in Plant-Hybridisation: Introduction and Concluding Remarks

Introductory Remarks引言#

Experience of artificial fertilisation, such as is effected with ornamental plants in order to obtain new variations in colour, has led to the experiments which will here be discussed. The striking regularity with which the same hybrid forms always reappeared whenever fertilisation took place between the same species induced further experiments to be undertaken, the object of which was to follow up the developments of the hybrids in their progeny.

为了得到新的花色变异而对观赏植物所作的人工授粉，其经验促成了这里将要讨论的这些实验。每当同样的物种之间进行授粉，同样的杂种类型总是一再出现，这种惊人的规律性，促使人们去做进一步的实验，目的是追踪杂种在其后代中的发展。

Those who survey the work done in this department will arrive at the conviction that among all the numerous experiments made, not one has been carried out to such an extent and in such a way as to make it possible to determine the number of different forms under which the offspring of hybrids appear, or to arrange these forms with certainty according to their separate generations, or to definitely ascertain their statistical relations.

纵观这一领域已做工作的人会确信：在为数众多的实验中，没有一个是以这样的规模、这样的方式进行的，能够确定杂种的后代以多少种不同的类型出现，或者能够把这些类型按它们各自所属的世代确切地排列起来，或者能够确定地查明它们之间的统计关系。

It requires indeed some courage to undertake a labour of such far-reaching extent; it appears, however, to be the only right way by which we can finally reach the solution of a question the importance of which cannot be over-estimated in connection with the history of the evolution of organic forms.

要着手一项范围如此之广的工作，确实需要一些勇气；然而，这似乎是唯一正确的道路，能让我们最终解决一个问题——就生物类型的进化史而言，这个问题的重要性无论怎样估计都不会过高。

The paper now presented records the results of such a detailed experiment. This experiment was practically confined to a small plant group, and is now, after eight years’ pursuit, concluded in all essentials. Whether the plan upon which the separate experiments were conducted and carried out was the best suited to attain the desired end is left to the friendly decision of the reader.

现在呈上的这篇论文，记录的就是这样一项详细实验的结果。这项实验实际上只限于一个小小的植物类群，经过八年的工作，现在在一切主要方面都已完成。至于安排和进行各项实验所依据的计划，是否最适合于达到所期望的目的，就留给读者善意地判断吧。

Concluding Remarks结语#

It can hardly fail to be of interest to compare the observations made regarding Pisum with the results arrived at by the two authorities in this branch of knowledge, Kölreuter and Gärtner, in their investigations. According to the opinion of both, the hybrids in outer appearance present either a form intermediate between the original species, or they closely resemble either the one or the other type, and sometimes can hardly be discriminated from it. From their seeds usually arise, if the fertilisation was effected by their own pollen, various forms which differ from the normal type. As a rule, the majority of individuals obtained by one fertilisation maintain the hybrid form, while some few others come more like the seed parent, and one or other individual approaches the pollen parent. This, however, is not the case with all hybrids without exception. With some the offspring have more nearly approached, some the one and some the other, original stock, or they all incline more to one or the other side; while with others they remain perfectly like the hybrid and continue constant in their offspring. The hybrids of varieties behave like hybrids of species, but they possess greater variability of form and a more pronounced tendency to revert to the original type.

把关于豌豆（Pisum）的观察，与这一知识领域的两位权威——克尔罗伊特和格特纳——在各自研究中所得的结果比较一下，不会不令人感兴趣。按照他们两人的看法，杂种在外观上要么呈现介于两个原始物种之间的类型，要么与其中这一个或那一个类型十分相似，有时几乎无法与之区分。如果用杂种自己的花粉授粉，它们的种子通常会长出各种与正常类型不同的类型。一般说来，一次授粉所得的个体，大多数保持杂种的类型，另有少数更像母本，也有一两个个体接近父本。不过，并非所有杂种都毫无例外地如此。有些杂种的后代，有的更接近这一个原始亲本，有的更接近另一个，或者全都更偏向某一方；而另一些杂种的后代则与杂种完全一样，并在后代中保持恒定。变种之间的杂种，表现与物种之间的杂种相同，但它们的类型变异性更大，回复到原始类型的倾向也更明显。

Gärtner mentions that in those cases where the development was regular among the offspring of the hybrids the two original species were not reproduced, but only a few closely approximating individuals. With very extended developmental series it could not in fact be otherwise. For seven differentiating characters, for instance, among more than 16,000 individuals—offspring of the hybrids—each of the two original species would occur only once. It is therefore hardly possible that these should appear at all among a small number of experimental plants; with some probability, however, we might reckon upon the appearance in the series of a few forms which approach them.

格特纳提到，在杂种后代发展有规律的那些情况下，两个原始物种并没有重现，只出现了少数与之十分接近的个体。在发展系列极为广泛时，事实上也不可能是别的样子。例如，对于七个相异性状，在一万六千多个个体——杂种的后代——之中，两个原始物种各自只会出现一次。因此，它们几乎不可能出现在少量实验植物之中；不过，我们或许可以有几分把握地预期，系列中会出现少数接近它们的类型。

We meet with an essential difference in those hybrids which remain constant in their progeny and propagate themselves as truly as the pure species. According to Gärtner, to this class belong the remarkably fertile hybrids Aquilegia atropurpurea canadensis, Lavatera pseudolbia thuringiaca, Geum urbano-rivale, and some Dianthus hybrids; and, according to Wichura, the hybrids of the Willow species. For the history of the evolution of plants this circumstance is of special importance, since constant hybrids acquire the status of new species. The correctness of this is evidenced by most excellent observers, and cannot be doubted. Gärtner had opportunity to follow up Dianthus Armeria deltoides to the tenth generation, since it regularly propagated itself in the garden.

在那些后代保持恒定、像纯种一样真实地繁殖自身的杂种身上，我们遇到了一种本质的差异。据格特纳说，属于这一类的有极其能育的杂种 Aquilegia atropurpurea canadensis、Lavatera pseudolbia thuringiaca、Geum urbano-rivale，以及一些 Dianthus（石竹属）杂种；据维丘拉说，还有柳树各物种之间的杂种。对于植物的进化史来说，这一情况特别重要，因为恒定的杂种取得了新物种的地位。这一点的正确性，有最优秀的观察者为证，不容怀疑。格特纳曾有机会追踪 Dianthus Armeria deltoides 直到第十代，因为它在园子里一直有规律地自行繁殖。

With Pisum it was shown by experiment that the hybrids form egg and pollen cells of different kinds, and that herein lies the reason of the variability of their offspring. In other hybrids, likewise, whose offspring behave similarly we may assume a like cause; for those, on the other hand, which remain constant the assumption appears justifiable that their fertilising cells are all alike and agree with the foundation-cell of the hybrid. In the opinion of renowned physiologists, for the purpose of propagation one pollen cell and one egg cell unite in Phanerogams into a single cell, which is capable by assimilation and formation of new cells to become an independent organism. This development follows a constant law, which is founded on the material composition and arrangement of the elements which meet in the cell in a vivifying union. If the reproductive cells be of the same kind and agree with the foundation cell of the mother plant, then the development of the new individual will follow the same law which rules the mother plant. If it chance that an egg cell unites with a dissimilar pollen cell, we must then assume that between those elements of both cells, which determine the mutual differences, some sort of compromise is effected. The resulting compound cell becomes the foundation of the hybrid organism, the development of which necessarily follows a different scheme from that obtaining in each of the two original species. If the compromise be taken to be a complete one, in the sense, namely, that the hybrid embryo is formed from cells of like kind, in which the differences are entirely and permanently accommodated together, the further result follows that the hybrids, like any other stable plant species, remain true to themselves in their offspring. The reproductive cells which are formed in their seed vessels and anthers are of one kind, and agree with the fundamental compound cell.

在豌豆上，实验表明杂种形成不同种类的卵细胞和花粉细胞，其后代的变异性原因就在于此。在其他后代表现相似的杂种中，我们同样可以假定有类似的原因；另一方面，对于那些保持恒定的杂种，似乎有理由假定它们的生殖细胞全都相同，并且与杂种的基础细胞一致。按照著名生理学家的看法，在显花植物中，为了繁殖，一个花粉细胞与一个卵细胞结合成单一的细胞，这个细胞能够通过同化作用和形成新细胞而成为一个独立的有机体。这种发展遵循一条恒定的定律，这条定律建立在那些于细胞中结成富有生机之结合的元素的物质组成和排列之上。如果生殖细胞属于同一种类，并与母株的基础细胞一致，那么新个体的发展就会遵循支配母株的同一条定律。如果碰巧一个卵细胞与一个不同的花粉细胞结合，我们就必须假定，在两个细胞中决定彼此差异的那些元素之间，达成了某种妥协。由此产生的复合细胞成为杂种有机体的基础，其发展必然遵循一种不同于两个原始物种各自所遵循的方案。如果把这种妥协看作完全的——就是说，杂种胚是由同类细胞形成的，差异在其中完全而永久地调和在一起——那么进一步的结果便是：杂种像任何其他稳定的植物物种一样，在后代中保持自身不变。在它们的子房和花药中形成的生殖细胞只有一种，并与那个基本的复合细胞一致。

With regard to those hybrids whose progeny is variable we may perhaps assume that between the differentiating elements of the egg and pollen cells there also occurs a compromise, in so far that the formation of a cell as foundation of the hybrid becomes possible; but, nevertheless, the arrangement between the conflicting elements is only temporary and does not endure throughout the life of the hybrid plant. Since in the habit of the plant no changes are perceptible during the whole period of vegetation, we must further assume that it is only possible for the differentiating elements to liberate themselves from the enforced union when the fertilising cells are developed. In the formation of these cells all existing elements participate in an entirely free and equal arrangement, in which it is only the differentiating ones which mutually separate themselves. In this way the production would be rendered possible of as many sorts of egg and pollen cells as there are combinations possible of the formative elements.

至于那些后代会变异的杂种，我们或许可以假定，在卵细胞和花粉细胞的相异元素之间也发生了妥协，其程度足以使作为杂种基础的细胞得以形成；然而，冲突元素之间的这种安排只是暂时的，并不贯穿杂种植株的一生。由于在整个生长期中，植株的习性看不出任何变化，我们必须进一步假定：只有在生殖细胞发育的时候，相异的元素才有可能从这种被迫的结合中解脱出来。在这些细胞的形成过程中，所有现存的元素以完全自由而平等的方式参与排列，其中只有相异的元素彼此分离。这样一来，就有可能产生与形成元素的可能组合一样多的卵细胞和花粉细胞种类。

The attribution attempted here of the essential difference in the development of hybrids to a permanent or temporary union of the differing cell elements can, of course, only claim the value of an hypothesis for which the lack of definite data offers a wide field. Some justification of the opinion expressed lies in the evidence afforded by Pisum that the behaviour of each pair of differentiating characters in hybrid union is independent of the other differences between the two original plants, and, further, that the hybrid produces just so many kinds of egg and pollen cells as there are possible constant combination forms. The differentiating characters of two plants can finally, however, only depend upon differences in the composition and grouping of the elements which exist in the foundation-cells of the same in vital interaction.

这里尝试把杂种发展中的本质差异，归因于相异细胞元素的永久结合或暂时结合，当然只能算作一种假说，确切资料的缺乏给它留下了广阔的余地。这一看法有一定的根据：豌豆提供的证据表明，每一对相异性状在杂种结合中的表现，与两个原始植株之间的其他差异无关；而且，杂种所产生的卵细胞和花粉细胞的种类，恰好与可能的恒定组合类型一样多。然而，归根到底，两种植物的相异性状只能取决于它们的基础细胞中、处于生命相互作用之中的那些元素在组成和组合上的差异。

Even the validity of the law formulated for Pisum requires still to be confirmed, and a repetition of the more important experiments is consequently much to be desired, that, for instance, relating to the composition of the hybrid fertilising cells. A differential element may easily escape the single observer, which although at the outset may appear to be unimportant, may yet accumulate to such an extent that it must not be ignored in the total result. Whether the variable hybrids of other plant species observe an entire agreement must also be first decided experimentally. In the meantime we may assume that in material points a difference in principle can scarcely occur, since the unity in the developmental plan of organic life is beyond question.

即使是为豌豆所表述的这条定律，其有效性也仍有待证实，因此很希望能重复其中较重要的实验，比如关于杂种生殖细胞组成的那一项。一个相异的元素很容易被单个观察者忽略，它起初也许显得无关紧要，却可能积累到在总的结果中不容忽视的程度。其他植物物种的可变杂种是否完全符合这一定律，也必须先由实验来判定。在此期间，我们可以假定，在实质问题上几乎不会出现原则性的差异，因为有机生命发展规划的统一性是毋庸置疑的。