How does a plant (like ivy or a tree) know where to create a branch?

Question

I was looking at our hedge and was wondering how it decides where to create a branch. What triggers it?

In: Biology

Answer 1

I don’t know if this a full answer, and probably I’m missing out something but anyway:
The edges of the steam that are exposed to sunlight will produce a growth hormone called auxin, which helps the cells at the tip of the stem to grow, as it grows the auxin will redistribute along the stem, such that only cells with sunlight will have auxin and will grow, while shaded parts of the stem won’t have auxin and thus won’t grow.
Hopefully this answers your question somewhat, and I didn’t make any mistakes.