522 



Plant Breeding. 



few cases by cottagers. It is, howev r er, work that requires 

 much perseverance, and, at certain seasons, much attention ; 

 though the demands that it makes on time necessarily 

 depend upon the extent to which it is carried on. 



For its successful performance it requires intelligent obser- 

 vation, a knowledge of the gardener's or farmer's require- 

 ments, delicate manipulation, and accurate recording, rather 

 than strenuous exertions. 



Two main lines are usually pursued to produce a new and 

 improved variety of crop-plant. One method of procedure,, 

 which has been successfully adopted by some of the best known 

 workers, is to make careful examination of the individual 

 plants in crops cultivated in the ordinary way, and from 

 these to make a selection of those that are distinguished by 

 superior merits. Such superiority may take the form of 

 yield, capacity to tiller, a high percentage of starch (as in 

 barley and potatoes) or of sugar (as in the case of turnips,, 

 swedes, and mangolds), capacity to ripen early, to resist 

 disease, &c. But whatever may be the object selected, it 

 must be kept steadily in view, and all individuals in the pro- 

 genythat fall short of the character that may have been set 

 up must be carefully eliminated. By intelligently pursuing 

 such a system of selection during a series of years a distinct 

 type or variety will be produced. 



The other method commonly pursued begins by arti- 

 ficially crossing two individuals whose superior qualities it 

 may be desirable to unite in a single variety. The seeds that 

 result from such a cross are sown, and it is generally found 

 that the resultant plants are extremely mixed in character. 

 Many are inferior to either of the parents, others occupy an 

 intermediate position, while a few may be superior to both. 

 It is the latter only that are reserved for subsequent cultiva- 

 tion, and from their progeny also many individuals must be 

 eliminated. In the course of time, however, the percentage 

 of inferior individuals becomes smaller and smaller, until, at 

 last, the variety comes true to type. 



In the main these two systems of improvement are the 

 same. The planes selected in the first case, may be natural 

 crosses, while, in the second, they are artificial crosses ; 



