. Heredity and evolution in plants . (Redrawn 1 So named from its discoverer, Quetelet (Ket-lay). As de Vries states:For a more exact demonstration a correction would be necessary, sinceobviously the larger beans fill up their compartment more than a similarnumber of small ones. io6 i v AND i m\ i\ PLANTS between the two limits or extremes, and is therefore oftenreferred to as a curve of frequency. It should be notedthat, in the case illustrated, the greatest frequency (in-dicated by the highest point of the curve) very nearlycoincides with the average dimension; in other words,
. Heredity and evolution in plants . (Redrawn 1 So named from its discoverer, Quetelet (Ket-lay). As de Vries states:For a more exact demonstration a correction would be necessary, sinceobviously the larger beans fill up their compartment more than a similarnumber of small ones. io6 i v AND i m\ i\ PLANTS between the two limits or extremes, and is therefore oftenreferred to as a curve of frequency. It should be notedthat, in the case illustrated, the greatest frequency (in-dicated by the highest point of the curve) very nearlycoincides with the average dimension; in other words, themore any given character departs from the average for thatc/iaracter, the less frequent is its occurrence. In another experiment, ears of corn, harvested fromthe same crop, were measured and found to vary in length. FIG. 52.—Curve of fluctuating variation (Quetelets curve), formed by-arranging 82 ears of corn in ten piles, according to the length of the extremes were and 9 inches. The ears were taken from unselectedmaterial from a field of corn. (After Blakeslee.) from 4)2 inches to 9 inches; the largest number of ears(20) were 7 inches long. The greater the departure fromthis length, in either direction, the fewer the individuals;for the lengths 4 inches and 9 inches the frequency waszero. When the ears were arranged in piles accordingto their length, the tops of the piles indicated the curveof frequency (Fig. 52). The curve of frequency indicates the quantitative dis-tribution of any character or quality when its occurrenceis dependent largely upon chance. This is strikingly EXPERIMENTAL EVOLUTION 107
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