[sdiy] help with basic circuit

[db]

I have basically used an existing circuit design for an LED driver (Ken 
Stone's)
But made a couple of changes to make it work for me..

On this schematic:

http://workingdistance.com/temp/led_circuit.jpg

I have reduced that resistor on the base from 100k as originally designed 
way down to 1k.
At 100k, the base voltage just wasn't high enough to switch this 
transistor, but at 1k, much better.

I don't really understand exactly what purpose this resistor serves, but 
eliminating it was not advised.
Can someone shed some light on what it does in this circuit, and why I 
really need it?

(Each time I lower the value, my LEDs get a little brighter.)

dennis.barton:skylab2000[socal]