IMPORTANCE OF ADAPTIVENESS IN PLANTS 497 



as those of soil and climate, may be transmitted to its descend- 

 ants. If it be so, then the origination of new forms of plants 

 by the inheritance of such characteristics must be extremely 

 common. 



474. Mutations of plants. Much attention has lately been 

 given to the occurrence among plants of seedlings which differ 

 in a marked way from the parents. It would involve too much 

 detail to describe the exact nature of the differences between 

 the seedlings of the evening primrose, 1 which has been most 

 studied in this connection, and its offspring, but they are as 

 great as those between an apple tree and a pear tree. Such 

 abrupt and extensive changes are called mutations. A few of 

 the most important facts so far known in regard to mutation are : 



1. New species 2 appear suddenly among the offspring of the 

 parent form. 



2. The individuals of the new species constitute only a small 

 per cent of any given brood. 



3. The new species reproduce themselves accurately, showing 

 no decided tendency to return to the parent form. 



475. Importance of adaptiveness in plants. It may be in- 

 ferred from Chapters xxxi and xxxiv that a premium is set on all 

 changes in structure or habits which may enable plants to resist 

 their living enemies or to live amid partially adverse surround- 

 ings of soil or climate. It would take a volume to state, even in 

 a very simple way, the conclusions which naturalists have drawn 

 from this fact of a savage competition going on among living 

 things, and it will be enough to say here that the existing kinds 

 of plants to a great degree owe their structure and habits to the 

 operation of the struggle for existence, together with their response 

 ~by means of variation to changes in the conditions ~by which they 

 are surrounded. How the struggle for existence has brought 

 about such far-reaching results will be briefly indicated in the 

 next section. 



1 (Enothera lamarckiana. 



2 For a definition of the term species, see Sec. 189. 



