STERILITY OF HYBRIDS 237 



sistent with actual specific difference; and of variations leading 

 to that consequence no clear indication has yet been found. 

 As an example of possible exceptions mention should perhaps be 

 made of the case of a giant form of Primula sinensis investigated 

 by Keeble. 3 It arose from a " Star " Primula of normal size, 

 and though fertile with its own pollen all attempts to fertilise 

 it with the pollen of other forms failed. Miss Pellew, who did 

 these fertilisations, tells me that very extensive trials were made, 

 and repeated in several seasons. Ultimately two plants were 

 raised from it fertilised with a plant of the strain from which it 

 sprang, and these proved sterile. In the light of modern expe- 

 rience the significance of such isolated instances is doubtful. 



All the strains known as " Giants " are, as Messrs. Sutton 

 have always found, more or less sterile, and their sterility is 

 presumably due to some negative defect. 



In regard to the fertility of Primula species there are several 

 paradoxes. For example the long-styled varieties, apart from 

 giants, are fertile with their own pollen, and for many years 

 short-styled plants have not been used in most strains. Auriculas 

 and Polyanthuses, on the contrary, are generally if not always 

 bred from short-styled plants, as the florists have decided that 

 the long-styled are inadmissible. Mr. R. P. Gregory tells me 

 that, though most strains of P. sinensis give seed enough 

 when only long-styled plants are used, he finds nevertheless 

 that when a " legitimate " union is made the amount of seed 

 usually increases much as Darwin observed. Darwin's state- 

 ment that plants of " illegitimate " origin are less fertile than the 

 " legitimately " raised plants is also in general confirmed by his 

 experience. To this rule there were some marked exceptions in 

 strains derived from long-styled plants, which though illegitimate 

 showed a high degree of fertility, but illegitimate unions between 

 short-styled plants always produced comparatively sterile off- 

 spring. I have no records of the behavior of Auriculas and 

 Polyanthuses. It would be interesting to know whether among 

 them pure strains of short-styled plants (dominants) have 

 appeared, and, if so, how their fertility is affected. Without 



Keeble, Jour. Gen., 1912, II, p. 173. 



