288 PHYSIOLOGICAL BOTANY. PART II. 



form and dimensions ; but this is at present mere con- 

 jecture. Not more than forty kinds of hybrids have 

 been found naturally produced in a wild state between 

 well-defined species, and all of these are described as 

 barren or incapable of perfecting their ovules ; so that 

 they can never be reproduced by seed, though they 

 may be propagated by other means. Numerous hy- 

 brids are continually produced artificially by horticul- 

 turists, for the purpose of obtaining choice flowers and 

 fruit ; and it has been asserted that many of these are 

 capable of fertilising their ovules, and thus of being re- 

 produced by seed. If this be really the case, it would 

 seem to be impossible for us to draw any distinction 

 between true species and hybrids. But sufficient atten- 

 tion has not hitherto been paid to this intricate subject, 

 to enable us to feel quite satisfied that these supposed 

 hybrids are any more than intermediate forms between 

 marked varieties or races of the same species. It 

 appears to have been ascertained that hybrids may 

 be fertilised by the pollen taken from one or other 

 of the parent species, and that the seed thus obtained 

 will produce plants intermediate between that species 

 and the hybrid, and thus a return may gradually .be 

 made to one of the original types. It has been equally 

 asserted of animals, that although mules never produce 

 young between themselves, yet a female mule may be- 

 come productive by a male of one or other of the parent 

 species. 



The rarity of wild hybrids is easily accounted for 

 by the fact, that so soon as the stigma has been affected 

 by the contact of the pollen, it becomes incapable of 

 transmitting an additional influence from any fresh 

 grains that may afterwards be applied to it ; and conse- 

 quently the chances of every stigma being first affected 

 by the pollen of its own stamens (if we except dioecious 

 species), is infinitely greater than its receiving any 

 influence from others. 



(296'.) Permanence of Specie*. Every thing that 

 has hitherto been written on the origin and limitation of 



