Chap. IX.] DEGREES OP STBRILITY. 7 



singular fact, namely, that individual plants of certain 

 species of Lobelia, Verbascum and Passiflora, can easily 

 be fertilised by pollen from a distinct species, but not 

 by pollen from the same plant, though this pollen can 

 be proved to be perfectly sound by fertilising other 

 plants or species. In the genus Hippeastrum, in Cory- 

 dalis as shown by Professor Hildebrand, in various or- 

 chids as shown by Mr. Scott and Fritz Miiller, all the 

 individuals are in this peculiar condition. So that with 

 some species, certain abnormal individuals, and in other 

 species all the individuals, can actually be hybridised 

 much more readily than they can be fertilised by pollen 

 from the same individual plant! To give one instance, 

 a bulb of Hippeastrum aulicum produced four flowers; 

 three were fertilised by Herbert with their own pollen, 

 and the fourth was subsequently fertilised by the pollen 

 of a compound hybrid descended from three distinct 

 species: the result was that "the ovaries of the three 

 first flowers soon ceased to grow, and after a few days 

 perished entirely, whereas the pod impregnated by the 

 pollen of the hybrid made vigorous growth and rapid 

 progress to maturity, and bore good seed, which vege- 

 tated freely." Mr. Herbert tried similar experiments 

 during many years, and always with the same result. 

 These cases serve to show on what slight and mysterious 

 causes the lesser or greater fertility of a species some- 

 times depends. 



The practical experiments of horticulturists, though 

 not made with scientific precision, deserve some notice. 

 It is notorious in how complicated a manner the species 

 of Pelargonium, Fuchsia, Calceolaria, Petunia, Rhodo- 

 dendron, &c., have been crossed, yet many of these 

 hybrids seed freely. For instance, Herbert asserts that 



