CHimeras: layers or zones???

[Megalodon]

Please help me!!!

I'm very confused at something... and I especially logged in this forum, to get help! (English is not my first language, as you might guess...)

Problem: chimeras

A shoot apical meristem can be divided into 3 layers (LI, LII, LIII). Now all cells derive from those layers and they even keep the order, when the divide. So when we have a leaf, those 3 layers are still there... no comes my problem:

There are two versions, and I don't know which one is correct:

- When you are talking about layers I,II,III is it meant now zones or layers? So if a mutation occurs in the second Layer, does it affect the layer below the epidermis of a leaf or does it affect the inner margin???

I could find both versions, and now I'm fully mixed up...

Could you please help me and give some examples???

Thank you!