Between inner
and outer surfaces there is a loose reticular interlayer, which is
made of criss-cross plate pieces and contains a plenty of pores of
10 lm. Because of its massive existence and large size, the pores
are easy to be found by SEM, which is called reticular honeycomb
structure. The reticular structure is mainly composed of protein,
sugar, lignin, cellulose and some metallic oxide.