Well I have read some of my recently aquired copy of "The Carnivorous Plants" and have read all of "Insectivorous Plants" and I must say they compliment eachother very nicely.
Darwin's book is basically a lab report proving plants can be carnivorous (although he says Insectivorous he uses meat to stimulate them). After extensivly proving D. rotundifolia was carnivorous he did some basic proofs for Dionaea, some Adquatic Utics, some Pings, some other Drosera and I think Androvanda.
"The Carnivorous Plants" is basically a lab report on the cell structure and make-up of Cps. It was not what I expected when I bought it but is very good if you are interested in all the different types of cells or rather functions. The descriptions are very acurate and many microscopic drawings are in the back of the book. Not real culture info is provided although Llyod does briefly re-prove carnivity (sp?) and has some experiments with growing medium. Don't quote me on this but I think he grew Androvanda in a slghtly Salty Solution for 2 years. It is very interesting if you want ot know how the plants function.
Unfortunatly the books do use the old names (S. drumondii, H. Macdonadle (sp?, and species now?), U. neglecta (sp?). So some reserce may be needed. But I would recommend buying both if you cna find them for cheep (ebay anyone?).