Chap. XVI. 



THE CROSSING OF VARIETIES. 



109 



capacity of this one variety has certainly been in some degree modified, 

 so as to approach in nature that of N. glutinosaP 



These facts with respect to plants show that in some few 

 cases certain varieties have had their sexual powers so far 

 modified, that they cross together less readily and yield less 

 seed than other varieties of the same species. We shall pre- 

 sently see that the sexual functions of most animals and plants 

 are eminently liable to be affected by the conditions of life to 

 which they are exposed ; and hereafter we shall briefly discuss 

 the conjoint bearing of this and other facts on the difference in 

 fertility between crossed varieties and crossed species. 



Domestication eliminates the tendency to Sterility which is general 

 with Species when crossed. 



This hypothesis was first propounded by Pallas, 26 and has 

 been adopted by several authors. I can find hardly any direct 

 facts in its support ; but unfortunately no one has compared, 

 in the case of either animals or plants, the fertility of an- 

 ciently domesticated varieties, when crossed with a distinct 

 species, with that of the wild parent-species when similarly 

 crossed. No one has compared, for instance, the fertility of 

 G-allus bankiva and of the domesticated fowl, when crossed 

 with a distinct species of Gallus or Phasianus; and the 



distinct species, mingled with a plant's 

 own pollen, if tlie latter be present in 

 sufficient quantity, have any effect. The 

 sole effect of niiagling two kinds of 

 pollen is to produce in the same capsule 

 seeds which yield plants, some taking 

 after the one and some after the other 

 parent. 



25 Mr. Scott has made some observa- 

 tions on the absolute sterility of a purple 

 and white primrose {Primula vulgaris) 

 when fertilised by pollen from the 

 common primrose (' Journal of Proc. of 

 Linn. Soc.,' vol. viii., 1864, p. 98) ; but 

 these observations require confirmation. 

 I raised a number of purple-flowered long- 

 styled seedlings from seed kindly sent me 

 by Mr. Scott, and, though they were all 

 in some degree sterile, they were much 

 more fertile with pollen taken from the 

 common primrose than with their own 



pollen. Mr. Scott has likewise de- 

 scribed a red equal-styled cowslip 

 (P. veris, idem, p. 106), which was 

 found by him to be highly sterile when 

 crossed with the common cowslip ; 

 but this was not the case with several 

 equal-styled red seedlings raised by me 

 from his plant. This variety of the 

 cowslip presents the remarkable pe- 

 culiarity of combining male organs in 

 every respect like those of the short- 

 styled form, with female organs resem- 

 bling in function and partly in structure 

 those of the long-styled form ; so that 

 we have the singular anomaly of the 

 two forms combined in the same flower. 

 Hence it is not surprising that these 

 flowers should be spontaneously self- 

 fertile in a high degree. 



26 ' Act. Acad. St. Petersburg,' 1780, 

 part ii., pp. 84, 100. 



