Thanks for the appreciation and sorry about the vagueness of the game. Here's where to find them, so beware of spoilers
Spoilers:
To reach the plant sample make a left u-turn at the further left corner when reaching the waterfall then make a right u-turn, then you will find some green sphere plants. To reach the meat sample go to the end of the spooky dark cave, then try to get back out, then something will happen.