INTRODUCTION 7 



it is found occasionally near abandoned 

 houses or in neglected back yards. The 

 sweet pea is undergoing similar critical 

 periods. In England, for instance, the 

 "Streak" already constitutes a serious 

 menace to profitable sweet pea culture. 

 The same conditions are beginning to pre- 

 vail in the United States, and several per- 

 plexing diseases now threaten the eco- 

 nomic existence of one of the most delicate 

 of flowers. 



