THROTJGH CUMULATIVE SEOKEGATION. 



265 



grandchildren any advantage over the self-fertilized grandchildren 

 raised from the self -fertilized children." " And, what is far 

 more remarkable, the great-grandchildren, raised by crossing the 

 grandchildren with a fresh stock, had no advantage over either 

 the intercrossed or the self-fertilized great-grandchildren. It 

 thus appears that Hero and its descendants differed in consti- 

 tution in an extraordinary manner from ordinary plants of the 

 same species." " If we look to the [ordinary] plants of the ninth 

 generation in table x., we find that the intercrossed plants [of 

 the same stock] were in height to the self -fertilized as 100 to 79, 

 and in fertility as 100 to 26; whilst the Colchester-crossed 

 plants [raised by crossing with a fresh stock] were in height to 

 the intercrossed as 100 to 78, and in fertility as 100 to 51."* 

 The Colchester-crossed plants were therefore in height to the 

 self-fertilized as 1 to '78 X '79, or as 1000 to 616, and in fertility 

 as 1 to '51 X "26, or as 1000 to 183 ; while the self-fertilized 

 descendants of Sco^o when crossed with the same fresh stock 

 not only had no advantage over those that had been continuously 

 self-fertilized for nine generations, but, as the details of the 

 experiment show, the advantage was on the side of the plants 

 raised from the self-fertilized seed. The experiment was con- 

 ducted under conditions decidedly unfavourable for the production 

 of healthy plants ; but, as it is usually found that the superiority 

 of crosses between varieties is most clearly brought to light when 

 the competitors are subjected to unfavourable circumstances, it 

 seems to furnish even stronger evidence of Segregate Vigour 

 being occasionally produced in the earliest stages of divergent 

 evolution, than would have been furnished if the same degree of 

 superiority in the self-fertilized plants had been obtained under 

 a less severe test. As the case is of unusual interest, I give the 

 details as recorded by Darwin : — 



" Several flowers on the self-fertilized grandchildren of Hero 

 in table xvi. were fertilized with pollen from the same flower ; 

 and the seedlings raised from them (great-grandchildren of 

 Hero) formed the ninth self-fertilized generation. Several other 

 flowers were crossed with pollen from another grandchild, so 

 that they may be considered as the ofispring of brothers and 

 sisters, and the seedlings thus raised may be called the inter- 

 crossed great-grandchildren. And, lastly, other flowers were 

 fertilized with pollen from a distinct stock, and the seedlings 

 ^ ' Cross- and Self-Fertilization,' pp. 47, 60, 61. 



