484 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



all degrees." ("Origin of Species," 6th ed., p. 262.) Again: 

 " The sterility of distinct species when first united, and that of 

 their hybrid offspring, graduates by an almost infinite number 

 of steps from zero (when the ovule is never impregnated and a 

 seed capsule is never formed) up to complete fertility. . . . This 

 high degree of fertility is, however, rare." (" Animals and Plants," 

 2nd ed., vol. ii. p. 163.) 



Fifteen years later we find Dr. Alfred Wallace enunciating 

 similar views. He writes : " One of the greatest, or perhaps 

 we may say the greatest, of all the difficulties in the way 

 of accepting the theory of natural selection as a complete 

 explanation of the origin of species has been the remarkable 

 difference between varieties and species in respect of fertility 

 when crossed. Generally speaking, it may be said that the 

 varieties of any one species, however different they may be in 

 external appearance, are perfectly fertile when crossed, and their 

 mongrel offspring are equally fertile when bred among them- 

 selves ; while distinct species, on the other hand, however closely 

 they may resemble each other externally, are usually infertile 

 when crossed, and their hybrid offspring absolutely sterile.''' 

 (" Darwinism," 1890, p. 152.) Dr. Wallace wrote these words 

 some seven years ago, but since that time some hundreds of 

 hybrid Orchids raised by hand from distinct species have flowered 

 in gardens. 



In consulting that admirable work of reference, the " Orchid 

 Hybrids," by Mr. George Hansen, of California, with the 

 second supplement made up to April 1, 1897, I find that there 

 are on record 733 hybrids from distinct crosses which have 

 already flowered, and of these 485 are the offspring of species x 

 species, and the remainder, 248 in number, are all the offspring 

 of hybrids. 



As far as the great Orchid Order is concerned, therefore, we 

 can hardly say now that " distinct species . . . are usually 

 infertile when crossed," and still less can we say that " their 

 hybrid offspring are absolutely sterile." 



Darwin laid much stress on the different degrees of sterility, 

 almost as much as on absolute sterility. In Orchids we have 

 not yet sufficient evidence to show that crosses between distinct 

 species produce fewer offspring than crosses between varieties of 

 the same species ; or, on the contrary, that they are equally 



