interesting field for research. Il is my hope Ihal a more Ihorough 

 investigation will be commenced there as early as the summer 

 of 1909. 



My heartiest thanks are due to the many contributors to this 

 work, for the warm interest they have shown, and for the devoted 

 labour and unwearying trouble they have given to the subject. 



EUG. WARMING. 



Botanical Garden, 

 Copenhagen, 



November 3rd, 1908. 



