HOW PLANTS ARE IMPROVED 107 



appear, for we know that a new variety is more apt to 

 produce new things than an old variety. 



If our new plant will not come true to seed, we propa- 

 gate it by cuttings, or by grafting, or by some similar 

 means, and it then usually comes true, We propagate 

 new varieties of potatoes, apples, and many other 

 plants in this way. 



Sometimes it is only one bud or branch of a plant that 

 produces something new (bud variation). An ordinary 

 rose sometimes produces a single branch bearing moss 

 roses. We propagate this branch by cuttings, and so 

 get a variety of moss roses. But this happens so 

 seldom that we cannot depend on it. 



Improvement by selection. By selecting the best 

 plants of corn every year (not merely the best ears), 

 and saving their seed, we find that our crops of corn 

 improve each year until a certain limit is reached. We 

 may double our crops before we reach the limit. If we 

 stop choosing the best ears each year, the quality of our 

 corn is soon no better than it was at first. 



Improvement by selection has this difficulty, that we 

 must keep on selecting in order to keep our improve- 

 ment, unless we should happen in the course of our 

 selection to find a variety which comes true to seed or 

 to some other method of propagation. In this case the 

 finder^usually saysjiejias made a new variety, when the 

 truth is that he has merely found one. 



Professor de Vries has found certain kinds of even- 



