I purchased 2 of what appear to be oil paintings signed Jan Van Huysum fecit
they are obviously reproductions of his work one is titled Gardener's
Gift and I am unsure of the 2nd one but it is similar. On the back of
the canvas it is written 1942 New York Graphic Society Ltd. all rights
reserved. 605. The paintings are 16"by20". My question is what is
their approximate value.

You have a canvas transfer.

New York Graphic Society is an art publisher.  They produce art prints
and posters (on paper) and also do canvas transfers.  Canvas transfers
are a chemical process whereby the image of the art print is 'lifted
off the paper' and permanently bonded to a high-grade artist canvas. 
It gives the 'appearance' of an original oil painting.

More on canvas transfers.
http://www.respree.com/canvas-transfers/index.html

You can buy them today for $100-$200.  Here's an example of one.
http://www.respree.com/product/pages/sku/LDINVJP-301

That said, if the item is in high demand and is no longer in print, it
might fetch something more, but I couldn't venture to say what. 
Market price is determined by how much people are willing to pay. 
Jump on eBay and see who else is selling it.  If nothing, there's
either no supply or no demand.

I know, it's not the 'million dollar' answer you looking for.

Hope this information has been helpful to you.