CONCLUSION 307 



immense majority carne to an end in the long-past 

 geologic ages. 



If we attempted to construct such a tree, say for our 

 twenty-six types, almost every branch would be marked 

 with a query. If the reader has gained some idea of the 

 difficulty and complexity of the profoundly interesting 

 problems which the comparative study of plants presents 

 to us, the object of this concluding chapter will have 

 been attained. 



