BLASTOGENIC VARIATIONS. 165 



the requirements of a species. The same is true of 

 Salvia sylvestris, a hybrid from 8. nemorosa and fira- 

 tensis, which abounds in dry meadows all over the low 

 country south of Vienna, and of Nuphar intermedium, 

 a hybrid from N. luteum and pumilum, which occurs in 

 the Black Forest, Russia, Sweden, and other localities. 

 It appears that a hybrid is sometimes found in company 

 with one parent only, or with one in one locality and 

 both in another; or sometimes even where both are 

 absent. 



Kerner estimated that something like a thousand 

 natural hybrids have been found in Europe during the 

 last forty years, but of these hybrids only a fraction 

 survive and multiply. 



As regards artificial hybrids, Hurst * has compiled a 

 list of genera from various authorities, and from his 

 own observations, and he finds that 91 distinct genera 

 are recorded in which fertile hybrids are known. In 

 only three, viz., Ribes, Polemonium, and Digitalis, were 

 the hybrids all quite infertile, and in none of them had 

 many experiments been made. 



Hurst also remarks that " during the past seven years 

 Mr. Reginald Young has been crossing inter se some 30 

 distinct species and 53 distinct hybrids in the genus 

 Paphiopedilum (Pfitz),and has . . . carefully recorded 

 no less than 849 crosses. Of these, taken together, 

 80.2 per cent, have proved fertile, i. e., produced good 

 seeds. Of 263 crosses between distinct species, 95 per 

 cent, were fertile. This seems to show that in this 

 genus crosses between distinct species are almost, if not 

 quite, as fertile as crosses between varieties of the same 

 * J. Roy. Horticult. Soc., xxiv. p. 90, 1900. 



