A stochastic partial differential equation in which the square root of the
solution appears as the diffusion coefficient is studied as a particular ca
se of stochastic evolution equations. Weak existence of a solution is prove
d by the Euler approximation scheme. The super-Brownian motion on [0,1] is
also studied as a Hilbert-space-valued equation. In this set up, weak exist
ence, pathwise uniqueness, and positivity of solutions are obtained in any
dimension d.