Britton and Roses classification of cacti:

http://www.cactuspro.com/biblio/en:britton_et_rose

All 4 volumes in electronic format!

+ many others :

http://www.cactuspro.com/biblio/

Bushpig

thank you, thank you. i was thinking about looking for something like this just the other day while working in the herbarium.

Not a problem, that website seems a great resource. What I would like ot know is what is the current definitive Cactus family key/guide of the present? And how much does it differ from this original work of Britton and Rose ?

Bushpig