87 



They may be almost identical in appearance, may ripen simultaneously, may 

 possess the same stiffness of straw and the same resistance against disease 

 yet one may thrive best on soils which are relatively light, warm and dry 

 while another may give better results on a heavier, colder and moister soil. 

 Were a variety of such composition sown on a field in which the soil is exceed- 

 ingly variable, it is conceivable that a better average may be obtained than 

 from an absolutely pure sort which demands more exact conditions. The 

 difficulty of knowing the real nature of the strains which go to make up a 

 mixed variety is such, however, as to render it an unsafe practice to depend 

 upon the possible virtues of a composite race. 



VI. METHODS OF WORK IN CEREAL BREEDING AT SVALOF 



The inability to determine the industrial worth either of an individual 

 or of a strain on the basis of morphological characters has led to the adoption 

 and gradual perfection of methods based upon direct judgment. 



Thus all plants selected as possible mothers from composite varieties, or 

 produced by artificial crossing must, if sufficiently promising, pass through 

 a long and arduous period of investigation, first in pedigree cultures, then in 

 preliminary trial plots and finally in the large comparative trial plots (See 

 Fig. 15). In all cases yield constitutes a leading basis of valuation in view 

 of the fact that this is regarded as a highly complex character, being 

 an expression of many different factors. 



Since it is seldom found practicable to work with more than from one 

 hundred to two hundred cultures from a given variety or crossing at the 

 same time and since it is of the utmost importance that the initial choice of 

 mother plants be made as advantageously as possible, two or three years of 

 mass-selection as a preliminary work is advised. 



The necessity of handling a large number of- plots of various sizes and ^ ze and 

 which represent different stages in the system of improvement, requires that arran d ement 

 the field work be arranged as systematically and economically as possible. p 

 The plots are therefore laid out in ranges with great care and precision. Each 

 plot in the experimental grounds is separated from its neighbor by a narrow 

 space which in all cases is sown with some other kind of culture plant such 

 as spring rye or flax (See Fig. 16) . In this way there is avoided any extra 

 stimulation of outer rows which otherwise would render the plots uneven and 

 abnormal. This growth of plants between plots is also believed to afford a 

 measure of protection not only against cross-fertilization, which even in 

 normally self-fertilizing cereals has always to be reckoned with, but also 

 against the accidental mixing of the product of different plots. 



The ranges occupied by the small pedigree plots are usually narrow, p edioree 

 1 . 50 metres (39") being the common width. The seed is planted in rows by cu u u res. 

 hand with the aid of the " marker," one seed being dropped in a place (See 

 Fig. 16). The distance between each row is 15 centimetres (about 6 inches), 

 while the plants within the row are 5 centimetres (about 2 inches) apart. 

 The object in planting with such exactness is to give each plant as nearly 



