81 



higher yielding sort by crossing, the principle has become to cross the two 

 highest yielding sorts with each other. This principle recognizes that the 

 specific yielding power of a sort is not to be regarded as a character in itself, 

 but rather as the result of a combination of many different factors. When 

 one crosses two sorts or, in other words, two combinations of characters, 

 which give the same average yield it is quite conceivable that the numerous 

 factors which determine yield can combine themselves in such a manner as 

 to produce sorts which are more productive than either of the parents." 

 (46, p. 169). 



A good example of the application of this principle is found in the 

 crossing between the two high yielding autumn wheat sorts Extra Squarehead 

 II X Tystofte Small. In oats the crossing between Victory and Nasgaard, 

 the two best yielding sorts in Sweden and Denmark respectively at the 

 present time, affords another good example, while in barley the high yielders 

 Hannchen and Gold have been crossed with the hope of obtaining among other 

 things a still further advance in yield. 



The above principle is also applied when seeking to improve upon 

 certain other practical qualities such as resistance against disease, strength 

 of straw, earliness of maturity, etc. 



From the above discussion it will be seen that crossings made at Svalof 

 are of two kinds in respect of the sorts used as parents, viz. : crossings between 

 pedigree sorts taken from the same old variety '(e.g., Victory and Danish 

 Nasgaard oats, both out of the old Probstier variety) and between sorts of 

 different origin. 



In all crossing work, care is taken ordinarily to avoid crossing sorts 

 which are too dissimilar in character. While it is fully recognized that 

 progress may be made by such a method, yet the difficulty of combining the 

 desirable characters of the parents is found to be greater in such cases. It 

 is considered safer practice not to try to obtain too much at the one time. 

 This principle also reduces one of the difficulties in crossing work, viz.: the 

 tendency toward sterility in oats and low quality in wheat. When widely 

 different oat sorts are crossed the sterility of the hybrids has always been a 

 great hindrance to progress. Thus, in crossing Great Mogul with Probstier 

 great sterility is met with. 



In order to take full advantage of all possible combinations which may Repeated 

 arise between the units involved in a crossing, repeated crossings may often crossings. 

 be made to advantage. Such repeated crossings have already been made at 

 Svalof. A good example is given in the cross Extra Squarehead II X Grenadier, 

 the latter being one of the parents of the former sort. 



It is a common observation that constancy after crossing is obtained 

 only gradually. The law of Mendel teaches that each single character in a . 



COYlStQTltCy 1YI 



certain proportion of the various combinations produced becomes constant new com . 

 in each generation, but since many characters may be involved it may binations. 

 happen that one character may become constant in a certain individual 

 while another character in the same individual may segregate. Thus a certain 

 wheat culture in the second generation (F 2 ) might possess a constant color 

 of chaff with an inconstant color or quality of kernel. Obviously the time 

 required to obtain full constancy in all characters depends largely upon the 



