110 Plant-Breeding 



and rye, and in some cases cross-fertilization is necessary, 

 all possibility of self-pollinization being precluded, as in 

 the case of hemp and other plants having the male and 

 female flowers on separate individuals. 



History of plant hybrids. Inasmuch as the sexuality of 

 plants was unknown, or at least very imperfectly under- 

 stood, prior to the last two centuries, while a knowledge 

 of the sex distinction of animals dates from the dawn of 

 human history, it is not surprising that while the hybridiz- 

 ing of animals was well understood by the ancients, they 

 did not know that crossing was possible with plants. 

 Experimental proof of the sexuality of plants was pub- 

 lished for the first time by Camerarius, December 28, 

 1691, and only after this discovery was the function 

 of pollen and its necessity for seed formation under- 

 stood. 



The earliest recorded observation of a plant hybrid is by 

 J. G. Gmelin toward the end of the seventeenth century; 

 the next is that of Thomas Fairchild, who in the second 

 decade of the eighteenth century produced the cross 

 which is still grown in literature under the name of 

 "Fairchild's Sweet William." It was a cross between the 

 carnation and sweet William. 



Linnaeus made many experiments in the cross-fertiliza- 

 tion of plants and produced several hybrids, but Joseph 

 Gottlieb Kolreuter (1733-1806) laid the real foundation 

 of our scientific knowledge of the subject. Later on, 

 Thomas Andrew Knight, a celebrated English horticul- 

 turist, devoted much successful labor to the improvement 

 of fruit trees and vegetables by crossing. In the second 

 quarter of the nineteenth century, C. F. Gartner made 



