LECTURE III 



ELEMENTARY SPECIES OF CULTIVATED PLANTS 



Recalling the results of the last lecture, we 

 see that the species of the systematists are not 

 in reality units, though in the ordinary course 

 of floristic studies they may, as a rule, seem to 

 be so. In some cases representatives of the 

 same species from different countries or re- 

 gions, when compared with one another do not 

 exactly agree. Many species of ferns afford 

 instances of this rule, and Lindley and other 

 great systematists have frequently been puz- 

 zled by the wide range of differences between 

 the individuals of a single species. 



In other cases the differing forms are ob- 

 served to grow near each other, sometimes in 

 neighboring provinces, sometimes in the same 

 locality, growing and flowering in mixtures of 

 two or three or even more elementary types. 

 The violets exhibit widespread ancient types, 

 from which the local species may be taken to 

 have arisen. The common ancestors of the 

 whitlow-grasses are probably not to be found 



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