Page:The New International Encyclopædia 1st ed. v. 05.djvu/708

CROSS-EXAMINATION. 612 CROSS-FERTILIZATION. exercised, especially in cases of cross-exaniina- tion of expert witnesses, whore it is necessary to show the standing and ability of the ex- pert. Previous mistakes in collateral matters not connected in any w'ay with the cause in issue have been allowed to be shown on this point. The right to cross-examination should Ix' ex- ercised inunediately after the e.xaminationin- chief; but it is in the discretion of the court, upon good reason shown, to allow the privi- lege at a later stage of the trial. See Evi- oence; Examination: Testimony: Witness: Trial. CROSS-FERTILIZATION. .V term usually applied l)y botanists tn the fertilization of flow crs by insects and other means, .so as to prevent too close in-and-in breeding. It has a wider significance, however, and may be applied to animals and the hiuuan races, in which latter case it is exemplified in the matter of race- crossing, or miscegenation. It is opposed to in- and-in breeding. There is no general term or word to exjiress the fact of cross-fertilization or intercrossing between dilVerent stocks of a single species. We might adopt and extend the meaning of the word cxofiaiiiii. used by anthro- pologists for marriage between members of dif ferent human tribes, and their term endofiamy for in-and-in breeding: or coin a new word, as Iieinntofintni/. for unions or marriages between blood-rehitives, and chidfitopaniy for cross-fer- tilization between members of different stocks of a single species. It is well known that in- and-in breeding among animals tends to sterility and degeneration : and. on the other hand, unions between different species, as well as members of widely distinct hunuin races — such as mar- riages between the white and negro or other backw-ard or primitive races — also tend to ster- ility, and assuredly to physical and moral de generation. Raee-marriage certainly is most unhappy in its results. While, as Darwin says, "nature abhors perpetual self-fertilization," the same is also true of misceaenation. Cros.s-Fertiliz.tion in Plants. As early as 1703 the German botanist Sprengel discovered the main facts, with many details, of the rela- tion of insects to floxers. He observed the won- derful adaptation of the structure of many fiowers to this or that species of insect visiting them : he satisfactorily proved that many kinds of flowers are cross-fertilized by insects, and that this was the object of the adaptations. He also observed that the presence of nectar and pollen attracted the insects and insured the con- tinuance of their visits. Several later writers showed that the' cross-fertilization of plants was beneficial to them. These discoveries were greatly extended by Darwin, who perceived the value of this process to the life and mainte- nance of the species. Darwin's observations were chiefly made on orchids, primulas, and so forth, and the suliject was greatly extended by Hermann Jtiiller, who, after many years of research, published his results on flowers and the structure and wonderful adaptations of the insects which visit them, in his elaborate volume entitled The Frrtlli~fttion of Floiccrs. It was further demonstrated by Darwin that the cross- fertilization of plants results in increasing the size, height, rapidity of growth, strength, and vi'_'or of the ]dniit. and in increasing its fertil- ity. As stated by Wallace iDaniiiiistii. p. ,30!)), these results were ])roduced iiumedialely, and not after several generations of crosses. Darwin planted seeds from cross-fertilized and self- fertilized plants on two sides of the same |>ot, which were exposed to exactly the same condi- tions. The result was that in most cases the difference in size and vigor in the two .sets was marked, while the plants arising from cross- fertilized parents also produced more and finer seeds. These experiments confirmed the experi- ence of breeders of domestic animals, where the evil effects of breeding members of the same lit- ter of dogs, or interiiuirriage between blood-rela- tives, result in sterility and degeneration. The results of cross-fertilization between flowers of the same species, and the great interest excited by Darwin in the subject, have led to a detailed study of the various contrivances by which flow- ers secure cross-fertilization, and this has led to the view that at least the irregular flowers, such as those of the ])ea, sage, and the orchid families, are. in reality, due to the visits of in- sects — a subject s])ecially worked out by the Rev. Cieorge Henslow in his Origin of Floral Structures. Modes of Securiufi Cross - Fertilization in I'ldiils. — Of the simpler modes there are four — viz. ( 1 ) By dichogamy, where the anthers and the stigma become mature or ready for fertiliza- tion at slightly dilTerent times on the same plant, as in the geranium, tliyme. arum, and others; (2) by the flower lieing self-sterile with its own pollen, as in the crimson flax: (3) by the sta- mens and anthers being so situated that the pol- len cannot fall upon the stigma, while it does fall upon some bee or moth which carries it to the stigma of another flower (malva): (4) by the male and female flowers being on different plants, as in dioecious flowers, the pollen being carried to the stigmas by the wind or by insects. See Pollination: BixinLEBEE. The more complex mode by Avhich exogamy is brought about is seen ( 1 ) in the case of the loosestrife (Luthrum salicnria) . a polymorphous flower, in which the stamens and pistil differ in length and position, and the different stamens in the same flower have widely different degrees of fertility when applied to the same stigma; (2) in the ease of the barberry, the irritable stamens of which spring up and dust pollen upon the insect that touches them; (3) in the case of others in which there are levers or jirocesses by w'hicli the anthers are mechanicaily brought down upon the head or back of an insect entering the flower in such a |)osition as to be carried to the stigma of the next flower it visits (Salvia, heath) : (4) in plants which have sticky secre- tion as milkwort (Polygala). which gets on the tongue or proboscis of an insect, and is borne to the stigma of another flower; '(5) in plants which have exploding anthers and other complex adjustments which thoroughly dust the insect, as in the pea family, e.g. Jledicago falcata ; (0) the entrapping of visitors in the spathes of Arum and Aristolochia : and (7) in the traps of the flower of .sclepias and Physianthus. which catch flies, Intttcrflies, and wasps by their legs: also the complex arrangements of orchids, described by Darwin in his Ferfilizaliou of Orchids. It ap- jiears that insects are attracted to those flowers which are largest and most gayly colored, the smaller, more inconspicuous not receiving so