  Let $\Omega$ be a non-singular syplectic form on some vector space $V$.
Denote by $S^{n}_{k}(\Omega)$ the set of all $k$-dimensional planes $s$ in $V$
such that the restriction of $\Omega$ onto $s$ is singular. For the cases when
$k=2,n-2$ a simple geometric characteristic of $S^{n}_{k}(\Omega)$ will be
described.
