280 SUMMARY OF MEASUREMENTS. Chai-. VIL 



by above five per cent, in height, or are inferior to 

 them, we may conclude that much the greater number 

 of the cfses do not form real exceptions to the rule, 

 that a cross between two plants, unless these have 

 been self-fertilised and exposed to nearly the same 

 conditions for many generations, gives a great 

 advantage of some kind to the offspring. Of the 

 twenty-six cases, at least -two, namely, those of Adonis 

 and Bartonia, may be wholly excluded, as the trials 

 were worthless from the extreme unhealthiness of the 

 plants. In twelve other cases (three trials with Esch- 

 scholtzia here included) the crossed plants either were 

 superior in height to the self-fertilised in all the other 

 generations excepting the one in question, or they 

 showed their superiority in some different manner, as 

 in weight, fertility, or in flowering first ; or again, the 

 cross-fertilised flowers on the mother-plant were much 

 more productive of seed than the self-fertilised. 



Deducting these fourteen cases, there remain twelve 

 in which the crossed plants show no well-marked 

 advantage over the self-fertilised. On the other hand, 

 Ave have seen that there are fifty-seven cases in which 

 the crossed plants exceed the self-fertilised in height 

 by at least five per cent., and generally in a much 

 higher degree. But even in the twelve cases just 

 referred to, the want of any advantage on the crossed 

 side is far from certain : with Thunbergia the parent- 

 plants were in an odd semi-sterile condition, and the 

 offspring grew very unequally; with Hibiscus and 

 Apium much too few plants were raised for the measure- 

 ments to Jbe trusted, and the cross-fertilised flowers of 

 Hibiscus produced rather more seed than did the self- 

 fertilised ; with Vandellia the crossed plants were a 

 little taller and heavier than the self-fertilised, but aa 

 they were less fertile the case must be left doubtful. 



