In reply to chickenpox: to photosynthesis all plants need light energy - those in caves will be in a position where they get light for a few hours of a day - and in jungles you get less vegetation lower, and much, much more in the canopy.
But when plants first start growing they do not - hence you plant them underground (no light) because the seed contains a tiny amount of nutrience that will help them grow out of the soil.
The story is still a load of.... beep...