Why he thought that bees could distinguish one kind of flowers from another?

Bees will try to stay on the same type of flowers when foraging for nectar and pollen. This is very much to the flowers' advantage because it ensures correct pollination. Bees can tell the difference between flowers both by smell and sight.

Using their antennae, bees have a very sensitive sense of smell: very many times more sensitive than our own. They also have good colour vision, but where we see colours from red to blue/violet, bees see colours from orange/yellow to ultra violet.