Rosie: there are a series of MATS that simulate x-ray photographs on whatever they are applied to. I can e-mail them if you'd like, but you might find them in free stuff. I think they'd do your job.
They come in several different colours.

Create flower.
Turn out the lights
Apply x-ray mats to flower.
Render.

Old-timers might want to come in here................

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All the Woes of a World by Jonathan Icknield aka The Bryster

And in my final hours - I would cling rather to the tattooed hand of kindness - than the unblemished hand of hate...