108 GENERAL REVIKW OF THE OROHIPE.E. 



is not true; it is not distinguishahle hy invariable characters. Species 



only have a constancy relational to the duration of the circumstances 



under which the individuals have lived." 



If we accept this definition of the species^ it is evident that 



plant forms of similar origin and structurally resembling each other 



may be brought under one species if safeguarded by the precaution 



not to allow too great expansion in application. On the other 



hand there is a tendency among some continental botanists and 



also among horticulturists both British and foreign to adopt as 



specific every deviation from a certain type ; the number of species 



of orchids may thence be indefinitely multiplied. 



The aflBnities of the Orchide^ are remote. Bentham places 

 them between Burmaniace^e with which they agree in the structure 

 of the seed, a family of over fifty species dispersed over the hotter 

 reo-ions of the globe in both hemispheres, not one of which is 

 probably in cultivation in other than botanic gardens, and Scitamine^, 

 a much larger family, also tropical and including genera with a 

 habit by no means unlike that of many orchids. The Irids have 

 often been likened to orchids on account of the remarkable and 

 gorgeous colours of the perianth segments of many species. 



