grass rendering problem - grass doesn't render behind transparent plane???

[nathanielshields]

I have been following this grass tutorial

using the hair and fur modifier and ran into a problem.

 

I have a number of trees in my scene that are just planes that I have applied a material on to (a bitmap of a tree with an opacity map).

when I render, the grass does not show up behind the plane despite the fact that it should be mostly transparent around the tree.

 

I have tried unticking the planes "visible to camera" tickbox in its object properties as well and when rendered it still renders the grass exactly the same. If I change its material to matte/shadow then I lose the tree image and therefore the shadow as well.

I am thoroughly confused… is this something to do with the scanline renderer? If anyone has any solutions that would be amazing, thanks

 

I am using 3ds max 2014. Rendering the main image in mental ray and the grass separately in scan line.