CHAP. V. CLARKIA ELEGANS. 169 



intercross in North Italy. Plants raised from a cross 

 between two varieties, differing only in the colour of 

 their flowers, grew much taller and were under un- 

 favourable conditions more vigorous than the self-ferti- 

 lised plants ; they also transmitted, when self-fertilised, 

 their superiority to their offspring. The many varieties 

 of the common Pea (Pisum sativum), though growing in 

 close proximity, very seldom intercross ; and this seems 

 due to the rarity in this country of the visits of bees 

 sufficiently powerful to effect cross-fertilisation. A 

 cross between the self-fertilised individuals of the same 

 variety does no good whatever to the offspring ; whilst 

 a cross between distinct varieties, though closely allied, 

 does great good, of which we have excellent evidence. 

 The flowers of the Broom (Sarothamnus) are almost 

 sterile if they are not disturbed and if insects are ex- 

 cluded. The pollen from a distinct plant is more 

 effective than that from the same flower in producing 

 seeds. The crossed seedlings have an enormous advan- 

 tage over the self-fertilised when grown together in 

 close competition. Lastly, only four plants of the 

 Ononis minutissima, were raised; but as these were 

 observed during their whole growth, the advantage of 

 the crossed over the self-fertilised plants may, I think, 

 be fully trusted. 



XV. ONAGKACEjE. CLABKIA ELEGANS. 



Owing to the season being very unfavourable (1867), few of 

 the flowers which I fertilised formed capsules ; twelve crossed 

 flowers produced only four, and eighteen self-fertilised flowers 

 yielded only one capsule. The seeds after germinating on sand 

 were planted in three pots, but all the self-fertilised plants died 

 in one of them. When the two lots were between 4 and 5 

 inches in height, the crossed began to show a slight superiority 

 over the self-fertilised. When in full flower they were measured, 

 with the following result:- 



