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. If 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 raised 

 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 Ipomoea purpurea every single inter 

 crossed plant exceeded in height its self-fertilised 

 opponent until the sixth generation ; and so it was 

 with Mimulus luteus until the fourth generation. Out 

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



* These fifteen species consist of Ipomcea purpurea, Mimulus luteus, 



Brassica oleracea, Reseda odorala Calceolaria, Verbascum thapsus, 



and lutea, Limnanthes douglasii, Vandellia nummularifolia, Lao 



Papaver vagum, Viscaria oculata, tuca sativa, and Zea mays. 

 Beta vulgaris, Lupinus luteus, 



* 



