CHAP. I. INTRODUCTORY REMARKS. 15 



for them and for the pairs, but have added up all 

 their heights, and thus obtained a single average. 



I long doubted whether it was worth while to give 

 the measurements of each separate plant, but have 

 decided to do so, in order that it may be seen that the 

 superiority of the crossed plants over the self-fertilised, 

 does not commonly depend on the presence of two or 

 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 off- 

 spring from intercrossed varieties being superior to 

 either parent-form, no precise measurements have been 

 given ;* and I have met with no observations on 

 the effects of crossing and self-fertilising the indi- 

 viduals of the same variety. Moreover, experiments ol 

 this kind require so much time mine having been 

 continued during eleven years that they are not 

 likely soon to be repeated. 



As only a moderate number of crossed and self- 

 fertilised plants were measured, it was of great impor- 

 tance to me to learn how far the averages "were trust- 

 worthy. I therefore -asked Mr. Galton, who has had 

 much experience in statistical researches, to examine 

 some of my tables of measurements, seven in number, 

 namely, those of Ipomo3a, Digitalis, Keseda lutea, 

 Viola, Limnanthes, Petunia, and Zea. I may premise 

 that if we took by chance a dozen or score of men 

 belonging to two nations and measured them, it would 

 I presume be very rash to form any judgment from 

 such small numbers on their average heights. But 

 the case is somewhat different with my crossed and 

 self-fertilised plants, as they were of exactly the same 



* A summary of these state- and Plants under Domestication, 

 ments, with references, may be chap, xvii., 2nd edit., 1875, voL 

 fonnd in my ' Variation of Animals ii. p. 109. 



