SQL Recursie view or stored procedure

I have a table with a recursive parent-child relation: Parent_ID refers to Line_ID

example of how that may look:
Line_ID . Parent_ID
------------------
1 . . . . . null -- higest item (no parent)
2 . . . . . 1
3 . . . . . 1
4 . . . . . 2
5 . . . . . 3
6 . . . . . 3
7 . . . . . 5
8 . . . . . 5
9 . . . . . 8
10 . . . . null

What i need is the following fucntion/view/..:
INPUT = any Line_ID
OUTPUT = table with ALL its LOWEST children (a Line_ID that has no Parent_ID refering to it)

example:
. . 1 . . . . . . . 10
|----|
2 . . 3
| . |---|
4 . 5 . .6
. .|-|
. .7 8
. . . |
. . . 9

1 would give 4, 6, 7, 9
2 would give 4
3 would give 6, 7, 9
4 would give null
5 would give 7, 9