Why is one marijuana plant smaller

A question from a fellow grower:

my two trees have grow in this say 5 months very good all I want to know is why is my one plant smaller than the other and how do I know if it is a male or female

plants from seed generally do that as they will have different phenotypes even though they are the same strain of cannabis, pretty much the only way around this is growing clones of the best growing plant you have, and they will grow pretty much at the same rate, male plants will develop pollen sacks (balls) if this happens get rid of it or it will pollenate your other plants becarefull doing this so to not break any sacks and pollenate your other plants.

Merry xmas, hope this helps.

The bigger one is probably a male if you don’t know the sex yet if it is be careful with it