The author's excellent 'powers of observation' [=ability to notice and pay close attention to things] are evident in the book's detailed descriptions.
The plants seem to have recovered from the disease, but they are still 'under observation'. [=someone is watching them carefully]
They're keeping him at the hospital 'for observation' [=so that doctors can watch him carefully] for another few days.
(..) Me? Speak up, for Christ's sake! I'm asking if you think my friend is making a tragic mistake. Actually, I don't know the Fitzgeralds that well. You're a writer. You make observations. You were with them all night! Could we not discuss my personal life in public? She's jealous of his gift, (..)2011 Midnight in Paris