CHAPTER XVIII. 



ON THE IMPROVEMKNT OF EACES. 



What has been stated in the preceding chapter, concerning 

 the preservation of the races of domesticated plants, is in some 

 measure applicable to their improvement; because the very 

 means employed to preserve those peculiairities of habit, which 

 render them valuable, will, from time to time, be the cause of 

 still more valuable qualities making their appearance. There 

 are, however, other points of great importance on which the 

 gardener has dependence. 



Sudden alterations in the quality of seedling plants often occur 

 from no apparent cause, just as those accidental changes, called 

 " sports," in the colour or form of the leaves, flowers, or fruit, 

 of one single branch of a tree, occasionally break out, we know 

 not why. Of these things, .physiology can give no account ; 

 but it is certain that, when such sports appear, they indicate a 

 violent constitutional change in the action of the limb thus 

 affected, which change may be sometimes perpetuated by.seed, 

 and always by propagation of the limb itself where propagation 

 is practicable. It is possible that even new forms of shrubs 

 might be procured by keeping these facts in view, and that 

 climbers might be deprived of their climbing habits, for it is 

 known that the handsome evergreen bush called the Tree Ivy, 

 which grows erect, with scarcely the least , tendency to climb, 

 has been procured by propagating the fruit-bearing branches of 

 trees of considerable age. 



A sport is a mutatio per saltwm, or, a sudden change of one 

 thing into another, different in some very striking respect, as 



