MK. C. DARWTX OX SPECIFIC DIFFERENCES IX PRIMULA. 413 



species of Primula would probably in some cases resemble other 

 species of the genus : thus I raised a red Primrose from seed from 

 a protected plant, and the flowers, though still resembling those 

 of the Primrose, were borne during one season on a long foot-stalk 

 like that of a Cowslip. 



With regard to the second class of facts in support of the Cow- 

 slip and Primrose being ranked as mere varieties (namely, the 

 well-ascertained existence in a state of nature of numerous link- 

 ing forms *), if it can be shown that the common wild Oxlip, which 

 stands exactly between the Cowslip and Primrose, resembles in 

 sterility and other essential respects a hybrid plant, and if it can 

 further be shown that the Oxlip, though in a high degree sterile, 

 can be fertilized by the pure parent species, thus giving rise to 

 still finer gradational links, then the presence of such forms in a 

 state of nature ceases to be an argument of any weight in favour 

 of the Cowslip and Primrose being varieties, and becomes, in fact^ 

 an argument on the other side. The hybrid origin of a plant in 

 a state of nature can be recognized, first, by its occurrence only 

 where both presumed parent forms exist or have recently existed ; 

 and this holds good, as far as I can discover, with the Oxlip ; but 

 the P. elatior of Jacq., which, as we shall presently see, consti- 

 tutes a distinct species, must not be confounded with the common 

 Oxlip. Secondly, by the supposed hybrid plant being nearly inter- 

 mediate in character between the two parent species, and espe- 

 cially by its resembling hybrids artificially made between the same 

 two species. Now the Oxlip is intermediate in character, and is 

 identical in every respect, except in the colour of the corolla, with 

 hybrids artificially produced between the Primrose and the Poly- 

 anthus, which latter is a variety of the Cowslip. Thirdly, by the 

 supposed hybrids being more or less sterile when crossed inter se\ 

 hut to try this fairly two distinct plants of the same parentage 

 should always be crossed ; for some pure species are more or less 

 sterile with pollen from the same individual plant ; and in the case 

 of hybrid dimorphic plants the opposite forms should be crossed. 

 Fourthly and lastly, by the supposed hybrids being much more 

 fertile when crossed with either pure parent-species than when 

 crossed inter se^ but still not as fully fertile as the parent; 

 species. 



Por the sake of ascertaining the two latter points, I transplanted 

 the group of wild Oxlips before alluded to into my garden. They 



# 



See an excellent article on this subject by Mr. H. C. Watson in the ' Phyto- 



logist,' vol. iii. p. 43. 



•t 



2 g2 



