What is That Large, Cannonball Shaped Fruit in the Tropical Greenhouse?

A picture of the fruiting limbs of Crescentia cujete, the Calabash tree, located in the north section of our tropical greenhouse. . 

Q. I'm a long-time garden member and would like to know the name of the large tree located at the bottom of the greenhouse that has several large and round dark green fruits? hanging on the tree.

A.  That's a Calabash tree. Crescentia cujete. It's in the same family as the glorious pink trumpet trees that you see blooming all around the Arboretum now. The fruit is inedible, but used commonly where the tree is native (Central and South America), or where it has been introduced and naturalized (India). 

See:
http://www.fruitsinfo.com/calabash-tree-tropical-fruits.php
https://toptropicals.com/catalog/uid/Crescentia_cujete.htm
http://www.tradewindsfruit.com/content/calabash-tree.htm