296 GENETICS IN RELATION TO AGRICULTURE 



The composite crossing of three or more varieties in an attempt to 

 effect a desired combination has been used successfully in small grains, 

 as well as in many flowers. Referring to grains alone, William Farrer 

 of Australia, A. N. Jones of the United States, and John Garton of 

 England have used this method successfully. In the opinion of Carleton, 

 Farrer leads all breeders in the production of hybrids that have come 

 into practical use. He continually practised composite crossing, as 

 many as six different varieties or subspecies entering into the ancestry 

 of many of his new sorts, some of which are of superior production or 

 milling quality as well as being disease resistant. 



Interspecific hybrids have frequently been produced by breeders 

 seeking some definite goal, occasionally with striking success, especially 

 among fruits. Even intergeneric hybrids have been reported, but the 

 known cases, with the exception of orchids, are of slight importance to 

 agriculture. For example, van der Stok secured a fertile hybrid between 

 corn and teosinte in the hope that some of the hybrids would bear good 

 sized ears and be resistant to chlorosis, a hope which was not, however, 

 realized. A few similar cases are known, particularly among cereals, 

 but very little use has been found for them. In fact, utilization of wide 

 crosses is rather definitely restricted to direct employment of the F\ 

 in cases where conditions of seed production are particularly favorable 

 for producing large quantities of hybrid seed or where the hybrid may be 

 propagated by clonal multiplication. 



Alfalfa culture appears to be capable of still further extension through 

 crossing of species. According to Fruwirth hybrids between common 

 alfalfa, Medicago sativa, and M . falcata are easily produced and occur 

 abundantly wherever plants of the two species grow near each other, 

 the crossing being effected by insects, especially bees. This was reported 

 in 1877 by Urban. These hybrid forms are known as M. media Pers. 

 (M. varia Martyn., M. versicolor Ser.). Seeds of these hybrids produce 

 forms that can be considered M. media, and, while flower color and pod 

 form are inconstant, the plants bear more seed and grow more luxuriantly 

 than M . falcata and adapt themselves to varied soil conditions. West- 

 gate has found good evidence that the well known hardy Grimm alfalfa 

 originated as a natural hybrid between these species, and that it was not 

 a product of acclimatization. Piper in 1908 called attention to the desir- 

 ability of securing hybrids between M. sativa and the yellow-flowered 

 Siberian species, and Hansen has recently determined the practicability 

 of producing such hybrids on a large scale by mixed field plantings. 

 Experts of the Bureau of Plant Industry of the U. S. Department of 

 Agriculture have made an enormous number of attempts to cross different 

 species of Medicago but utterly without success except in the case of 

 falcata and sativa. Selfed sativa and especially media (falcata x sativa) 



