4H 



VASCULAR CRYPTOGAMS. 



surface. The lowest of the three cells thus formed, which Janczewski calls the 

 basal cell (Fig. 294, below e), subsequently divides in the same manner as the cells 

 of the surrounding tissue, and thus contributes to the formation of the ventral wall 

 of the archegonium which is completely embedded in the tissue of the prothallium. 

 The most external of the three primary cells gives rise to the wall of the neck of the 

 archegonium (Fig. 294, A, hh), by dividing crosswise into four cells from which the 



Fig. 293.— Antheridia of Adiantum. Capillus-Veneris (X SSo), in longitudinal optical section ; / not yet ripe ; 

 // the antherozoids alrt ady mature ; /// the antheridium burst, the parietal cells greatly swollen radially, the 

 antherozoids mostly escaped ; / prothallium, a antheridium, s antherozoid, b the vesicle containing starch- 

 grains. 



four rows of cells of which the neck of the archegonium consists are produced by 

 oblique divisions. The anterior wall of the neck (that is, the wall which is directed 

 towards the apex of the prothallium) grows more rapidly than the opposite wall and 



fi A. 



Fig. 294.— Young archegonia of Pteris serrtilata (after Strasburger) ; e the central cell, h h the neck, k the canal-cell. 



becomes convex. Accordingly, the number of cells in the anterior row is larger 

 than that of the posterior row, in the former it is usually six, in the latter, four. 



From the middle one of the three primary cells the central cell and the canal- 

 cell of the neck are derived, that is, the axial row of cells of the archegonium. 

 Whilst the wall of the neck is being formed, this middle cell becomes pointed above 

 and penetrates between the cells of the neck (Fig. 2^4, A); the pointed portion is 



