548 General Botany 



United States and the West Indies. All these families are com- 

 paratively modern. 



The laurel family {Lauracece) , to which the European laurel, 

 sassafras, cinnamon, and spice bush belong, is a very ancient 

 family. Its fossil record extends back to the lower Cretaceous. 

 Today its members are scattered widely over the earth, with 

 numerous species in Brazil and southeastern Asia. 



Hundreds of examples of this kind might be cited, and all would 

 afford evidence that related plants are distributed over the earth's 

 surface as though they had originated in some one locality and 

 had then spread to other regions. Sometimes they became di- 

 versified chiefly at their center of origin ; sometimes as they spread 

 they formed secondary centers of diversification. But in all 

 cases the species that occur along a given line of migration are 

 closely related. 



The geography of plants, therefore, furnishes a second line of 

 evidence that existing plant species have been derived from 

 preexisting species. 



Comparative anatomy and physiology. One of the most strik- 

 ing proofs of evolution is the remarkable similarity of the cells, 

 tissues, and organs that make up plants belonging to diverse 

 groups. However much they may differ in superficial appearance 

 and in detail, they all have a common plan and organization. 

 The diversity has been brought about through modification in one 

 direction or another. Even more remarkable is the similarity 

 of the physiological processes underlying life, not only in all 

 plants, but in animals also. 



Life histories. Except on the basis of evolution it would be 

 impossible to account for the fact that throughout the whole 

 plant kingdom the life histories are so strikingly similar. As we 

 pass from simple plants to the flowering plants, the life histories 

 become more and more complex. Attention has already been 

 called to these facts, and it is only necessary here to repeat that 

 the changes in life history have been made by comparatively 



