INTRODUCTION 13 



plant pathology is based. That these eras in our science 

 are often almost coincident with great historic epochs is 

 also significant. So sharp usually has been the change 

 from one era to the next that we may wi h considerable 

 accuracy designate the year, or decade at least, which 

 marks the passing of one and the inauguration of another. 

 I shall designate these eras as follows: (1) the Ancient 

 Era; (2) the Dark or Middle Era; (3) the Pre-modern or 

 Autogenetic Era; (4) the Modern or Pathogenetic Era, 

 and (5) the Present Era. 



Each era divides itself more or less sharply into periods 

 — phases in the development and crystallization of the 

 prevailing point of view of the epoch. Since the thought 

 of each period, in the development of this, as of other 

 sciences, has been strongly influenced, in fact often 

 molded, by the life and works of some one man, I shall, 

 as far as practicable, designate each period by a name 

 indicating its dominating personality, following in general 

 the nomenclature used by Jensen (1909). 



