  Let $G$ be the group of $\mathbb R$--points of a semisimple algebraic group
$\mathcal G$ defined over $\mathbb Q$. Assume that $G$ is connected and
noncompact. We study Fourier coefficients of Poincar\' e series attached to
matrix coefficients of integrable discrete series. We use these results to
construct explicit automorphic cuspidal realizations, which have appropriate
Fourier coefficients $\neq 0$, of integrable discrete series in families of
congruence subgroups. In the case of $G=Sp_{2n}(\mathbb R)$, we relate our work
to that of Li [15]. For $\mathcal G$ quasi--split over $\mathbb Q$, we relate
our work to the result about Poincar\' e series due to Khare, Larsen, and Savin
[16].
