On canonical representations for stochastic processes of multiplicities one and two

Let $x_1(t)$ and $x_2(t)$, $t\in R^1$, be orthogonal linearly regular stochastic processes of multiplicity one, and $x(t)=x_1(t)+x_2(t)$.
The relation between the closed linear spans of the processes values, $H(x_1)$ and $H(x_2)$, and $H(x)$, is studied.