6o 



MOSSES AND FERNS 



CHAP. 



especially in the lower half of the embryo. In the upper part 

 periclinal walls appear, but not at any stated time, so far as 

 could be made out, and the first ones do not, as Leitgeb asserts, 



Fig. 21.— Targionia hypophylla (L.)- A, Longitudinal section of the venter of a ripe archegonium, 

 X500; B-E, development of the embryo, seen in longitudinal median section— B, two-celled, 

 D, four-celled stages, X500, except E, which is magnified 150 times ; F, nearly median section of 

 the upper part of an older embryo, X 250. 



necessarily determine the separation of the archesporium, as in 

 the Corsiniese. The growth now becomes unequal, the cells in 

 the central zone not dividing so actively, a marked constriction 



