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Show 14 lNTRODUCTORY REMARKS. CHAP. I. plants raised from the seeds re1naining after the pairs had been planted) unless the tallest plants on each side seemed fairly to represent the average difference between those on both sides. It has, how v r, some great advantages, as sickly or accidentally injur d plants, or the offspring of ill-ripened seed , are thus eliminated. When the tallest plants alone on ach side were measured, their average height of course xcoods that of all the plants on the same side taken too·ether. But in the case of the much crowded plant rais d from the remaining seeds, the average height of tho tallest plants was less than that of the plant in pairs, owing to the unfavourable conditions to which they were subjected from being greatly crowded. ~, or our purpose, however, of the comparison of the cro c1 and self-fertilised plants, their absolute height sio·nific. little. As the plants were measured by an ordinary English standard divided into inches and eighths of an ineh, 1 have not thought it worth while to change th fractions into decimals. The average or mean heights were calculated in the ordinary rouo-b m thud by adding up the measurements of all, and dividing the product by the number of plants measured; th result being here given in inches and decimais. .A.s the different species grow to various heights, I have always for the sake of easy comparison given in addition the average height of the crossed. plants of each species taken as 100, and have calculated. the averao·e hei ryht of the self-fertilised plant in relation to this ~tand:rcl. With respe.ct. to the crowded plants raised. from the seeds rem~1n1ng after. the pairs had been planted, and of wh1ch only some of the tallest on each side were measured, I have not thought it worth while to complicate the results by giving separate averages CHAP. I. INTRODUCTORY REMARKS. 15 for. the~ and for the pairs, but have added up all theu herghts, and thus obtained a single average. I long doubted whether it was worth while to give the. measurements of each separate plant, but have decrd~d .to do so, in order that it may be seen that the su penon ty of the crossed plants over the self-fertilised does not comrnonl y depend on the presence of two 0 ; three extra fine plants on the one side, or of a few very poor plants on the other side. Although several observers have insisted in general terms on the offspring from intercrossed varieties beino· superior to e1' th e r parent-form, no precise measuremebn ts have been given;* and I have met with no observations on t~e effects of crossing and self-fertilising the indivr~ ual~ of the same variety. Moreover, experim-ents of th1s _krnd requ~re so much time-mine having been c_ontrnuecl dunng eleven years-that they are not hke~ y soon to be repeated. As only a moderate number of crossed and selffertilised plants were measured, it was of great importance to me to learn how far the averages were trustworthy. I therefore asked Mr. Galton, who has had much experience in statistical researches, to examine so1ne of my tables of measurements, seven in number, n~mely, . those of Ipomcea, Digitalis, Reseda Iutea, v rola: .Lrmnanthes, Petunia, and Zea. I may premise that rf we took by chance a dozen or score of 1nen belonging to two nations and measured them, it would I presume be very rash to form any judgment from such sma~l numbers on their average heights. But the ?as~ _Is somewhat different with my crossed and self-fert1hsed plants, as they were of exactly the same * A summary of th ese state~ ents! with references, may be touudm my' Variation of Animals and Plants under Domestication ' chap. xvii., 2nd edit. 1~75 vol ii. p. 109. ' , . |