398 MEANS OF CROSS-FERTILISATION. CHAP. X. 



the cowslip. From the flowers thus treated thirty 

 seedlings were raised, and all these without exception 

 bore reddish flowers ; so that the effect of the plant's 

 own pollen, though placed on the stigmas twenty- 

 four hours previously, was quite destroyed by that of 

 the red variety. It should, however, be observed that 

 these plants are heterostyled, and that the second union 

 was a legitimate one, whilst the first was illegitimate ; 

 but flowers illegitimately fertilised with their own pollen 

 yield a moderately fair supply of seeds. 



We have hitherto considered only the prepotent 

 fertilising power of pollen from a distinct variety over 

 a plant's own pollen, both kinds of pollen being 

 placed on the same stigma. It is a much more re- 

 markable fact that pollen from another individual of 

 the same variety is prepotent over a plant's own pollen, 

 as shown by the superiority of the seedlings raiser! 

 from a cross of this kind over seedlings from self- 

 fertilised flowers. Thus in Tables A, B, and C, there 

 are at least fifteen species which are self-fertile when 

 insects are excluded ; and this implies that their stigmas 

 must receive their own pollen ; nevertheless, most of 

 the seedlings which were raised by fertilising the non- 

 castrated flowers of these fifteen species with pollen 

 from another plant were greatly superior, in height, 

 weight, and fertility, to the self-fertilised offspring.* 

 For instance, with Ipomcea purpurea every single inter- 

 crossed plant exceeded in height its self-fertilised 

 opponent until the sixth generation ; and so it was 

 with Mimulus luieus until the fourth generation. Out 

 of six pairs of crossed and self-fertilised cabbages, every 



* These fifteen species consist of Iponuea purpurea, Mimidus luteut, 



Bra&sica oleracea, Reseda odorala Calceolaria, Verbascum thapsus, 



and lutea, Limnanthes douglasi'', Vandellia nummularifolia, Lue- 



J'apaver vagum, Viscaria oculata, tuca sativa, and Zea mays. 

 Beta vulgaris, Lupinus luteus, 



