  We investigate the time series of the degree of minimum spanning trees
obtained by using a correlation based clustering procedure which is starting
from (i) asset return and (ii) volatility time series. The minimum spanning
tree is obtained at different times by computing correlation among time series
over a time window of fixed length $T$. We find that the minimum spanning tree
of asset return is characterized by stock degree values, which are more stable
in time than the ones obtained by analyzing a minimum spanning tree computed
starting from volatility time series. Our analysis also shows that the degree
of stocks has a very slow dynamics with a time-scale of several years in both
cases.
