AP BIOLOGY

Detailed explanation-1: -Regressive (Down-Grade) Evolution Theory: According to this theory the primitive bryophytes were mass-like in appearance. They had erect leafy shoot with radial symmetry like that of mosses. From mosses the evolution proceeded through Acrogynous Jungermanniales, Anthocerotales and Marchantiales.

Detailed explanation-2: -Similarities Between Bryophytes And Pteridophytes Both plants consist of the heteromorphic alternation of generations. They are multicellular sporangia. The cuticle is present in both the plants. Sexual reproduction takes place due to the presence of oogamous.

Detailed explanation-3: -In 1855 the leading British transcendental anatomist Robert Knox proposed a theory of retrogressive development according to which the human embryo could give rise to ancestral types or races and the animal embryo to other species within the same family.