  We make a study of unipotent elements in a connected reductive group over an
algebraically closed field with emphasis on the case where the characteristic
is a bad prime. We try to see how much of the theory of Dynkin-Kostant extends
to this case. We also study the variety of Borel subgroups containing a
unipotent element and prove a purity property for its cohomology in certain
cases in bad characteristic.
