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 prothalHum. 
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 
FfG. 293.— Antiieridia of Adiantmn Capitliis-Ve7ieris (X SSo), in long-itudinal optical section ; / not yet fipe J 
// the antherozoids air. ady mature ; /// tlie antheridiuni 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 
FU>. 294.— Young archegonia of Pteris scrriilata (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 
