Algebraic groups associated with Cartan Lie $p$-algebras

For all irreducible $p$-representations $\rho$ of simple Lie $p$-algebras $W_n$, $S_n$, $H_n$ and $K_n$ a description is given of groups generated by one-parameter subgroups of the form $\exp t\rho(x)$, where $x$ is a homogeneous element of the algebra for which $x^p=0$.
Bibliography: 11 titles.