Steady-state and dynamic experiments have been performed on solutions containing cellulose dissolved in monohydrate of N-methylmorpholine N-oxide (NMMO). The dependence of the zero-shear viscosity eta(0), and of the terminal relaxation time tau(c), on concentration, average degree of polymerization (<(DP)over bar>) and temperature are discussed. The behavior of this semi-rigid, polymolecular polymer in solution differs from that of flexible monodisperse ones. The slope of the plot of log (eta(0)) versus, on the one hand, log (c) at fixed molecular weight (<(DP)over bar>)=600, and, on the other hand, log (<(DP)over bar>) at fixed concentration (c=5% w/w) are equal to 4.6 and 5 respectively, instead of 3.4 in the concentrated region. Experimental data for the shear modulus were fitted using the classical Doi-Edwards equation with a log normal distribution of relaxation time. This distribution is compared to the distribution of DP.