How can I tell a male pear tree from a female?

If you have a look to these photos of pear flowers

http://www.aphotoflora.com/Pyrus%20commu...

http://www.shotshop.com/index.php/page/7...

http://www.cas.vanderbilt.edu/bioimages/...

you can see, there are both male ( stamens, red ) and female ( pistills, light green ) organs in the same flower: pear trees are bisexual.
How can I tell a male pear tree from a female?
by its little pear balls...lol
skates