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Show 460 GENERAL RESULTS. CHAP. XII. favourable results than a mere exchange of seeds. vVe have se n in my experiments how wonderfully the offspring profited in height, weight, ~ardinoss, and fertility, by crosses of this kind. For Instance, plants of Ipomcea thus crossed were to the intercrossou plants of the same stock, with which they grew in competition, as 100 to 78 in height, and as 100 to 51 in fertility; and plants of Eschschol tzia similarly coin pared were as 100 to 45 in fertility. In comparison with selffertilised plants the results are still Inoro striking; thus cabbages derived from a cross with a fresh stock were to the self-fertilised as 100 to 22 in weight. Florists rna y learn from the four cases which have been fully described, that they have the power of fixing each fleeting variety of colour, if they will fertilise the flowers of the desired kind with their own pollen for half-a-dozen generations, and grow the seedlings under the same conditions. But a cross with any other individual of the same variety must be carefully prevented, as each has its own p culiar constitution. After a doz n generations of self-fertilisation, it is probable that the new variety would remain constant oven if grown under s mew hat dif.C rent conditions; and there would no lona r b any necessity to guard against inter-b . crosses betw en the individuals of the same vanety. vVith respect to mankind, my son George has endeavoured to discov r by a statistical invostigatio~ * whether the marriaaos f :firs't cousins arc at all Injurious, although fhis is a degree of rolationsh~p which would not be obj ctecl to in our domest~c animals; and he has come to the conclusion from his own res arches and those of Dr. Mitchell that the evidence as to any evil thus caused is conflicting, but * 'Journu.l of Statistical Soc.' nightly Review,' June 1875. June 1875, ]J· 153; und 'Fort- CHAP. XII. GENERAL RESULTS. 46l on the ':hole .points to its being very small. Frmn the facts .given In th~s volume we may infer that with mankind the marnages of nearly related f h persons, some o . w ose paren. t.s and ancestors had l1' ve d un d er very different conditions, would be much less injurious than that of persons who had always lived in the same place and followed the same habits of life. Nor can I s~e reason to doubt that the widely different habits of hfe of men and women in civilised nations, especially amongst the upper classes, would tend to counterbalance any evil from marriages between healthy and somewhat closely related persons .. .Under a theoretical point of view it is some gain to science to know that numberless structures in herm~ phrodite plan.ts, and probably in hermaphrodite a.ninlals, are special adaptations for securing an occasional cross between two individuals; and that the advantages from such a cross depend altogethe1• on the beings ~hich are united, or their progenitors, having had then sexual elements somewhat differentiated, so that the embyro is benefited in the same manner as is a mature plant or animal by a slight change in its conditions of life, although in a much higher degree. Another and more important result may be deduced fro~ my observations. Eggs and seeds are highly. serviceable as a means of dissemination, but we now know that fertile eggs can be produced without the aid of the male. There are also many other methods by which organisms can be propagated asexually. Why then have the two sexes been developed, and why do males ~xist which cannot themselves produce offspring? The answer lies, as I can hardly doubt, in the great gpod which is derived from the fusion of two somewhat differentiated individuals ; and with the |