How much science, how much fiction?

I've been editing my environmental novel this week.  My main two characters are conservationists, professional scientists, so I needed to put a reasonable amount of correct science in the book to make them look credible.  But I also wanted to shake things up a bit.  The planet they're on is very definitely out of the ordinary.  It has trees which can see, move, and speak.  How was I going to create these without looking completely ridiculous?  

Some things were easier than others.  Beefing up the usually slender mycelium threads that run beneath trees into sizeable cords was the easy bit.  That then allowed me to claim that they transmitted a sizeable electric current - enough to run a forest Internet.  But eyes were a different matter.  I've decided the trees would have calcite eyes.  I've taken the primitive eyes trilobites used to see with and adapted them for tree vision.

So far, so good.  But calcite - transparent crystals of calcium carbonate - doesn't belong in trees.  Trees are made of cellulose and lignin, and they don't have skeletons, so they don't have any handy calcite lying around. 

And this is where the hand-waving of fiction comes in.  I haven't tried to explain how the trees have evolved like that.  I've merely noted that they're totally different from any other tree my character Kelli has ever seen,  and then I've put her to work finding out how these trees work.

The same is true of the telepathic big cats who, very handily, just happen to speak the humans' language.  Their ancestors were dumped on the planet by humans.  These cats have inherited telepathic abilities from them, and another entity on the planet has supplied knowledge of humans' current language.  All very convenient for moving the story along.

And some of my humans are telepaths, so they can talk to the cats, who tell them some vital history they weren't aware of.  Again, I've done some hand-waving, not attempting to explain how the humans became telepaths.

I think I've got the mix right.  There's enough real science mixed in with my flights of fancy to prevent the ideas in the novel from becoming totally ridiculous.