474 GENERAL MORPHOLOGY OF PLANTS 



ones, if it does not already present great variation among the 

 individuals it is necessary to bring it into a variable state. The 

 plant may vary only with reference to percentages of a desirable 

 quality of product. In this case continued selection would only 

 maintain a high degree of excellence in this respect. It may be 

 desirable to develop a different variety which may possess this 

 same quality in a higher state of excellence or to work for new 

 qualities. If the variety to be experimented on is a comparatively 

 stable type it is first necessary to get it out of this state of sta- 

 bility, otherwise no satisfactory improvement could be made. It 

 is necessary to " break the type," as plant breeders say. This 

 may be done in one of several ways according to conditions. 

 Methods much employed are: first, by cross pollination of 

 closely related varieties ; second, by cross pollination of a variety 

 with its species; third, by cross pollination of closely related 

 species. The hybrids from these crosses are likely to show 

 greater variation than either of the parent forms. The type may 

 often be still farther broken, or greater variation may often be 

 induced, fourth, by crossing the hybrid with one or both of its 

 parents. Variation is resorted to because the greater the range of 

 variation the greater chance there is of obtaining the desired 

 qualities among the individuals. Variation can also be induced 

 in other ways. It is well known that when feral plants are taken 

 into cultivation and given better food, and competition is largely 

 removed, the plants tend to vary, and often this variation extends 

 over a wide range. So when plants are introduced in new 

 localities where the conditions are different, variation often is the 

 result. This fact is often taken advantage of and leads to a fifth 

 principle according to which the type can be broken, namely, by 

 securing seed from a different locality. This seed from a distant 

 locality when planted side by side with seed of plants which in 

 their own locality are quite stable and show little variation, often 

 produces plants which are very variable and thus affords a wide 

 range for the selection of varieties which can be still farther 

 improved by selection. This is often combined with a sixth 

 method, that of crossing individuals of the same variety which 



