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Show 8 VARIATION CHAP, I. No case is on record of a variable being ~easing to be variable under cultivation. Our oldest .cu~tivated plants, sue h as w heat, still often yield new varieties :· ao .u r oldest domesticated animals are still capable of rapi Improve-ment or modification. It has been disputed at what period of life the causes of variability whatever they may be, generally act; whether duri~g the early or late period of. development of the embryo, or at the instant of conception. Geoffroy St. Hilaire's experiments show that unnatural treat~~nt of the embryo causes monstrosities ; and mo~st:osi~Ies cannot be separated by any clear line of _dist~nctwn from mere variations. But I am strongly Inchned to suspect that the most frequent cause of variability ~ay be attributed to the male and female reproductive elements having been affected prior t~ the. act ?f conception. Several reasons make me beheve ~n this; but the chief one is the remarkable effect which confinement or cultivation has on the functions of the reproductive system; this system appearing to be. fa~ more susceptible than any other part of t!1~ organi~ation, to the action of any change in the conditiOns of hfe. Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement even in the many cases when the male and female unit~. How many animals there are which will not breed, thouO'h living long under not very close confinement in th~ir native country ! This is generally attributed to vitiated instincts ; but how many cultivated plants display the utmost vigour, and yet rarely or never seed ! In some few such cases it has been found out that very trifling changes, such as a little ~ore or l~ss water at some particular period of growth, w1ll determine whether or not the plant sets a seed. I cannot here enter on the copious details which I have collected on CHAP. I. UNDER DOMESTICATION. this curious subject ; but to show how singular the laws are which determine the reproduction of animals under confinement, I may just mention that carnivorous animals, even from the tropics, breed in this country pretty freely under confineme_nt, with the exception of the plantigrades or bear family; whereas, carnivorous birds, with the rarest exceptions, hardly ever lay fertile eggs. Many exotic plants have pollen utterly worthless, in the same exact condition as in the most sterile hybrids. When, on the one hand, we see domesticated animals and plants, though often weak and sickly, yet breeding quite freely under confinement ; and when, on the other hand, we see individuals, though taken young from a state of nature, perfectly tamed, long-lived, and healthy (of which I could give numerous instances), yet having their reproductive system so seriously affected by unperceived causes as to fail in acting, we need not be surprised at this system, when it does act under confinement, acting not quite regularly, and producing offspring not perfectly like their parents or variable. Sterility has been said to be the bane of horticulture; but on this view we owe variability to the same cause which produces sterility; and variability is the source of all the choicest productions of the garden. I may add, that as some organisms will breed most freely under the most unnatural conditions (for instance, the rabbit and ferret kept in hutches), showing that their reproductive system has not been thus affected; so will some animals and plants withstand domestication or cultivation, and vary very slightly-perhaps hardly more than in a state of nature. A long list could easily be given of" sporting plants;" by this term gardeners mean a single bud or offset, which suddenly assumes a new and sometimes very different character from that of the rest of the plant. B3 |