82 



Creating of 



plant 



populations. 



number of different characters concerned in the crossing. When crossings 

 are made between closely related forms, it is not difficult to obtain a sufficient 

 degree of constancy in selected combinations in a relatively short time. 



Selection as practised with the progeny of artificial crossings corresponds 

 closely in principle with that followed in the isolation of lines (line-breeding) 

 from a common population. Practically the only difference between the two 

 cases is that in the application of line-breeding to artificial crossing products, 

 selection is continued until sufficient constancy is reached in the selected 

 combinations. The details of the method of selection practised in such cases 

 will be discussed later. 



While it is undoubtedly of great importance in the majority of cases 

 that well known and thoroughly tested pedigree sorts be used as parents in 

 crossing work, yet on account of the great length of time which is often neces- 

 sary before such sorts are available, it is not advised to forego crossing work 

 entirely during this time. Rather is it believed that crossing should continue 

 as a parallel work, providing known old varieties which seem to offer possi- 

 bilities along this line are available. A good illustration to show that a 

 common unselected variety may sometimes be used to advantage in crossing 

 work is found in a crossing between the wheat sorts Pudel and the common 

 Swedish velvet chaff. 



- The actual labor and time required in connection with crossing work 

 during the first two years is so small that it is regarded a good practice to 

 always have on hand crossing material of at least the second generation (F 2 ) , 

 from promising sorts which are under trial, in order that just this much time 

 may be saved should the results of such trials justify the prosecution of 

 further work with a given cross. This plan has been followed at Svalof for 

 some years and in several cases has resulted in saving considerable time. 



Still another course of procedure in crossing work, especially with 

 autumn w r heat, has begun to be practised at Svalof, viz., the creating of 

 populations (46, p. 169). Two known sorts are crossed and the whole 

 progeny from all second and succeeding generations is sown together en 

 masse. The object of this plan is to allow the severe conditions of winter 

 and early spring to either destroy or expose the weaknesses of as many of 

 the more delicate combinations as possible. In the latter case the breeder 

 is given an opportunity of assisting nature in her work of elimination by 

 practising a form of mass-selection. While there is thus effected in a very 

 simple manner, a gradual weeding out of a great mass of unfit combinations, 

 the progeny of a crossing at the same time gradually assumes the character 

 of an ordinary mixed population, the different combinations becoming 

 automatically constant as time passes. The advantages of working with 

 constant forms will be appreciated by all breeders as will also the fact that 

 through the above arrangement the number of combinations which may arise 

 through the repeated segregation of inconstant forms in each succeeding 

 generation will have increased immensely. 



The above system has been followed with the wheat crossing 0235 (out 

 of Selected Squarehead) and.0^70 (out of English Stand-Up).* 



*See Vagledning pa 1909 ars forsoksfalt vid Svalof, p. 8, Field Number 42. 



