How does cotyledon height reflect on root system?

Salutations everybody,

While lurking around i’ve seen a lot of what seemed like “stretching” of the stem below the cotyledon when compared to this, for example:

Since this subject once captivated my attention long ago there’s possibly a related a question on my mind that remains without an answer, hence i’d like to propose an idea for some future contest - it’s a 2-parts thing actually:

1) What’s the lowest cotyledon while it remains healthy?

2) What hint(s) can we get from a lower cotyledon vs rooting?..

Good day, have fun!! :peace: