You're seeing 'reaction wood'. Hardwood and softwoods react in opposite ways. I'll leave it to you to research the topic, it's much too complicated for me to type out.
we see trees bent to where there is more light. That makes it convenient to say that they grow 'towards' light. But, from a really nerdy and botanical sense they're really growing 'away' from shade. It has to do with how much and where trees produce growth and agreeing on what 'growth' means.
In both cases the description of what I'm talking about is very nerdy and only makes sense for arborists and other treenerds.
Don't even get me going on the more accurate term of 'sealing' in reference to how trees react to wounds. Using the word 'healing' isn't accurate. Healing connotes the generation of new tissues to replace the damaged tissues. It's a biological term. Sealing is a botanical term connoting how trees react to wounds by growing new tissues to isolate wounds as well as generate chemical reactions to decay. If you want to learn more research "CODIT" from the work of Dr. Alex Shigo.
Nerd out...coffee is ready!