\begin{tikzpicture}[node distance=1.1cm,>=stealth',bend
  angle=45,auto,transform shape]

  \tikzstyle{place}=[circle,thick,draw=red!75,fill=red!20,minimum size=5mm]
  \tikzstyle{transition}=[rectangle,thick,draw=blue!75,
  			  fill=blue!20,minimum size=4mm]

  \tikzstyle{every label}=[black]

  \begin{scope}
    % Petri net  Process
    \node [place] (ppc1) [tokens=0] [xshift=0cm]{}
    ;
    \node at (ppc1.west) [left] {};
    
%    \node [transition] (tp1) [right of=ppc1,dash pattern=on 2pt off 2pt]  {}
%      edge [post,bend right,dash pattern=on 2pt off 2pt] (ppc1)
%    ;
%    \node at (tp1.south) [below] {{$source$}};

    \node [transition] (tpc1) [below of=ppc1] {}
      edge [pre]  (ppc1)
    ;
    \node at (tpc1.west) [left] {};

    \node [place] (ppc2) [below of=tpc1] {}
      edge [pre] (tpc1)
    ;
    \node at (ppc2.west) [left] {};

    \node [transition] (tpc2) [below of=ppc2] {}
      edge [pre]  (ppc2)
    ;
    \node at (tpc2.west) [left] {};

    \node [place] (ppc3) [below of=tpc2] {}
      edge [pre] (tpc2)
    ;
    \node at (ppc3.west) [left] {};
    
%    \node [transition] (tp2) [right of=ppc3,dash pattern=on 2pt off 2pt] {}
%      edge [pre,bend left,dash pattern=on 2pt off 2pt] (ppc3)
%    ;
%    \node at (tp2.north) [above] {{$target$}};
  \end{scope}

\end{tikzpicture}