PLANT-BBEEDING 267 



of the species, and the more marked the variation, the 

 stronger is the tendency to reversion. 



436. How to fix desirable variations. — A fixed vari- 

 ation, i.e., a variation of which the progeny resembles 

 the parent in all important characters, becomes a variety 

 (21) as this word is used with reference to cultivated 

 plants. Varieties that produce their more important 

 characters when grown from seed are often called races. 

 There are two possible ways of fixing a desirable variation : 



(a) By propagating the plant by division (345) . — This 

 enables us to maintain a given variation through many 

 generations with comparatively little deviation from the 

 form with which we started (341). Our varieties of 

 fruits, potatoes, geraniums and many flowering plants, 

 and of many of. our finest ornamental trees and shrubs 

 are fixed in this manner. It is well known that varie- 

 ties propagated in this way rarely " come true " from 

 seed, i.e., their seed does not usually produce plants of 

 the same variety as the parent. But it is not practi- 

 cable to propagate all plants by division. With plants 

 more conveniently propagated from seed, such as the 

 cereals, Indian corn and most garden vegetables, we 

 may fix varieties to a certain limit. 



(6) By persistent selection toward an ideal type. — For 

 example, if we discover a single pea plant in a row of 

 peas that produces earlier pods than any other plant 

 and we desire to fix this variation, we should save all 

 the peas from this plant and sow them the next spring. 

 Most of the plants from this seed will probably be later 

 than the parent, but two or three of them may equal 

 it in earliness. We should save the seeds from the earliest 

 plant again, and continue this selection through several 

 seasons. It would be well to note the incidental char- 



