242 BOTANY: PRINCIPLES AND PROBLEMS 



634. Do you think that evohitionary change would take place more 

 rapidly in a region freely exposed to immigration from without, or in a 

 comparatively isolated region? Why? 



635. The great land mass of Europe and Asia is believed to have been 

 the center of evolution for many types of animals and plants now found 

 in other parts of the world. Why? 



636. Are the most widely spread plant species the oldest, do you 

 think? Explain. 



637. In consequence of the "struggle for existence" and the "sur- 

 vival of the fittest," why is it that in a given locality one species does 

 not exterminate all the others and compose the entire vegetation? 



638. Name a few of the changes in the natural vegetation of the 

 world which have been brought about by civilization. 



REFERENCE PROBLEMS 



102. Give an example of a new variety of cultivated plant which has 

 recently been developed by plant breeders. 



103. About how long do geologists estimate that life has existed on the 

 earth? 



104. What are the great geological periods into which the ancient history 

 of the earth has been divided by geologists? 



105. Summarize the life and work of Lamarck and state his important 

 contributions to botany. 



106. Summarize the life and work of de Vries and state his important 

 contributions to botany. 



107. Give the derivation of the following terms and explain in what way 

 each is appropriate: 



Evolution Fossil Orthogenesis 



