8 JuLV, 1908.] Improvement of Cereah by SelcctiO}i and Crossing. 405 



THE IMPROVEMENT OF CEREALS BY SELECTION 

 AND CROSSIXC. 



{Continued from page 2qi .) 

 D. Me Alpine, Vegetable Pathologist. 



II.— Crossing. 



As already pointed out in 'treating of Hallett's " pedigree-cultures," 

 there is a limit to the possibilities of preelection even wlien the best grain of 

 the best ear of the best plant is ccntinuousl) chosen for propagation. The 

 wheat plant may be nourished to its fullest capacity, but it can only absorb 

 a I erlain quantit) of food material and produce a number of grains which 

 it cannot exceed. If more were attempted the vegetative powers of the 

 plant would be overtaxed or its nature would require to be completely 

 changed. Still the highest possible average is an improvement. But when 

 this highly developed plant is crossed with another variety, always assum- 

 ing that the choice of parents has been judicious, it is claimed that further 

 improvement may be effected. 



It has to be remembered that the wheat-plant is self-fertilized ; that 

 before the florets ha\e opened, the pollen, which produces the male element 

 or sire, is deposited on the so-called female organ of the same flower and 

 fertilization is the result. The weakening effects of this perpetual in- 

 breeding have been counteracted by the constant artilicial selection of the 

 i)est ; but when new blood is introduced by means of a suitable cross, 

 then the whole system of the .plant is re-invigorated. 



The cross-fertilized plant is sometimes called a cross-breed or hybrid. 

 It is a recognized practice now to apply the term "hybrid " to all in- 

 uniduals which arise from a cross between parents, no matter whether 

 tbie\ belong to distinct species or represent only different races or varieties. 

 iMany writers, however, including Darwin, distinguished between the off- 

 spring resulting from species and that from races or varieties of the same 

 species, restricting the term " hybrid " to the former and applying the 

 term " mongrel " to the latter. The use of the general term hybrid will 

 allow of the principles of breeding to be included under the general head- 

 uig of Hybridization. 



We will first of all consider some of the practical results of crossing, 

 as obtained by some of our successful breeders, and then endeavour to 

 understand the principles on which they are based. " The aim of crossing 

 IS the combination of the desirable qualities of two or more species and 

 \arieties into one strain and the elimination of undesirable qualities." The 

 combination of the beneficial qualities and the elimination of the detri- 

 mental qualities by breeding out is the chief end in view, and it is in 

 tliis combination of characters that the novelty lies. 



But while the production of new varieties is one of the objects of 

 crossing, it is not the only one, and perhaps the most important is to infuse 

 new vigor into an existing variety and thus improve it. In the case of 

 wheat, where self-fertilization is the rule, the cr>ossing between different 

 plants of the same variety, either when grown under similar conditions or 

 better when grown under different conditions, gives rise to stronger and 

 more productive off'spring. Bv a judicious selection of parents, the type 



