334 
.AMARYLLIDACEiE. 
on the upper surface of a tuber ; I cannot bring to mind 
whether the Dioscoreae do so or not, and I have not access to 
any of that genus at present, but I observe from the engrav- 
ing that Testudinaria does not ; and, if Dioscorea does, that 
circumstance will furnish a stronger feature of generic dis- 
tinction than any which has been yet noticed ; but we must 
look far beyond this natural order to judge of its validity in 
limiting the affinity of vegetables, and we should find it dis- 
tinguishing Caladium from Arum, which shews that it cannot 
be available as a high grade of separation. 
