Abstract: From the phyllogeny, We found that the Wood Which came first should be gryptogamic wood of the arboreous ferns, such as Lopidodondron Sphenophyllum, etc, which were extinet long before. Those which survived are all phanegamic wood, including conifer wood of Gymnosperm and broad-leaved wood of Angiosperm, which appeared after the palaeozoic era and Mesozoic era. The Gryptogamic wood are primary and have exarch and mezarch Primary xylem; while the phanegamic wood are evolutionary and have endarch Primary Xylem (with exleption). After Studying on the cotyledon no des of the Seedlings of Angiosperm, we have found that between the cotyledon node and epicotyl shool zone there are still meristimatic tissues which have no relations with moristem on tap. In the splitting process, these tissues can control the split of the primary vascular tissues and make them evolve from mezarch primary Xylem of seed ferms to endarch primary Xylem of Gymnosperm and Angiosperm. Thus, the secondary phanegamic wood can be evolved from the Primary Gryptogamic wood.

Key words: Cotyledon node zone theory, Wood structure, Gryptogamic wood, Phanegamic wood