What determines the number of spines on a holly leaf?

This practical was developed for the Scottish Highers and is in the appropriate format, but the protocol can equally well be used for other UK specifications.

Holly leaves are capable of producing spines. This investigation is to see if there is a relationship between the number of spines on a leaf and its height above the ground. If such a relationship does exist, is there a reason for it?

Download the full protocol from the link on the right.