I went to Institute of Nature Study in Meguro today. Admission fee was 300 yen ($3.09 €2.36) for adults and free for under high school students. Institute of Nature Study is a kind of botanical park to preserve the nature of Tokyo. Park keepers does not plant any plants, just keep the nature as is. The park in on the way to the climax forest of Tokyo. In other words, you can see native flora of Tokyo.
The following is landscape of the park.
Lizard of Tokyo
The web site of Institute of Nature Study is here.