My first impression of [Peter] Latz the previous afternoon was that of a tall, lanky, bearded figure lying naked in the shade of his bedroom on the telephone to a fellow botanist.  He lay under a languid ceiling fan, a muted Beethoven symphony on the hi-fi just at the threshold of audibility.  Outside, under the shadow of a hat brim, his ice-blue eyes shone with quiet mischief.  Latz is an ethno-botanist and has lived all his life in the Arrernte country of central Australia.