Hi yvesjaye,
I can't comment on the plant model or material, so I'm sorry to hijack your thread and deviate from the topic....
I've noticed you pop up a lot on the forum in recent days. You're obviously new to Corona and the forum, and possibly new to 3DS max too.
I'd recommend, rather than asking us many tedious questions, you first acquaint yourself with the Corona support website. Additionally, watching youtube tutorials will take you a long way. Specifically, I'd recommend watching beginner tutorials for Corona. Also, of course, rather than asking super specific questions (such as this one), first do a search in the forum to see if other similar problems have arisen.
I'm sorry to dissuade you from discussion in the forum, but I honestly don't think you'll learn much by coming to us with every little hurdle you encounter. Have a play in 3ds max and corona, try to figure the problem out yourself.
Good luck.