We study singularities of solutions of the heat
equation, that are not necessarily isolated but occur only in a single
characteristic hyperplane. We prove a decomposition theorem for certain
solutions on
![$D_+=D\cap({\mathbf R}^n\times ]0,\infty[)$](img1.gif)
,
for a suitable open
set
D, with singularities at a compact subset
K of

,
in terms of Gauss-Weierstrass integrals. We use this to prove a
representation theorem for certain solutions on
D+, with
singularities at
K, as the sums of potentials and Dirichlet
solutions. We also give conditions under which
K is removable for
solutions on

.