We introduce a graphically based formalism for parallel system designs, covering both functional and stochastic behaviour. This paper focuses on the combination in one formalism of characteristics of two major approaches to formalisms for concurrent systems, namely Process Algebras and Petri Nets. We define a general form of composition on nets with stochastic delays for transitions. This incorporates place and transition fusion. Then, following the general method of CCS, we define inference rules for deriving the behaviour of a composed net from the behaviour of its components. We give a number of examples to illustrate this synthesis of Petri Nets and Process Algebras.