VlJl PREFACE. 



all require a cool climate^ because the mass of them disap- 

 pears below 9000 feet^ how erroneous would be that conclusion 

 when we find a species peculiar to a zone 5000 feet lower^ and 

 possessing a mean temperature 16° higher. 



It must not^ however^ be supposed that temperature is the 

 only influence to be considered in the cultivation of these plants; 

 it should in all cases be regarded in its relation to humidity, 

 light, and atmospheric pressure ; but unfortunately we have 

 little information concerning the first, and the two last are 

 beyond our control. 



Acton Green, 

 Nov.l,lU6. 



