using columns for labels

[Giuseppe G. N. A. <Giu...@ct...>]

Hi,

how can one use the content (in general, an alphanumeric one) of a given 
column to produce a label?

Say, something of the kind:

plot 'datafile.dat' u 1:2 t "$3" w p

where $3 would be expected to pick the content of the 3rd column
(presently, it just gives the string $3 invariably).

Thanks.

Giuseppe.