28 GENUS PALLAVICINIA 



five peripheral ones. Occasionally, as in the Marchantiales, there are six 

 peripheral cells, but this is not usual. 



The axial cell divides first by a transverse wall, and from the ventral 

 cell arises by a subsequent division, the egg-cell, and the ventrai canal cell 

 (Fig. 14, K). The upper of the two original axial cells next has cut off 

 from it a terminal, or cap-cell (Fig. 14, D). This cell may divide almost 

 at once by two intersecting walls, into four cells arranged quadrant-wise 

 when seen in cross-section ; but in P. radiculosa this quadrant division is 

 not always evident, and the cap-cell undergoes a considerable number of 

 divisions which add to the upper part of the neck (Fig. 14, G, H). There 

 is thus a limited apical growth of the neck, as well as growth due to inter- 

 calary divisions of the original neck-cells. This apical growth suggests 

 that found in the moss-archegonium, but is much less prominent, and does 

 not give rise to any of the canal-cells, which are all derived by division 

 from the original neck canal-cell. 



Gayet [1] states that he found a similar apical growth in a large 

 number of liverworts, but his statements have not been confirmed by sub- 

 sequent investigations. (See Campbell [1].) 



The original neck canal-cell gives rise to five or six in the mature 

 archegonium (Fig. 14, I). The neck may become very much elongated 

 (Fig. 15), a single row of the outer cells containing as many as forty 

 cells. The neck, in these elongated archegonia, usually becomes twisted. 



Up to the time of the separation of the egg-cell and ventral canal- 

 cell, the outer part of the venter consists only of a single layer of cells 

 (Fig. 14, /, /) ; but it later becomes divided into two layers by a series 

 of periclinal divisions (Fig. 14, L). 



P. Levieri differs mainly from P. radiculosa in the earlier separation 

 of the cap-cell, and the regular division of this into quadrants, so that 

 usually the cap-cell does not contribute to the growth in length of the 

 archegonium-neck (Fig. 15, C-E). 



The archegonia of P. radiculosa are larger than those of P. Zollin- 

 geri, and the periclinal walls in the venter seem to be formed at a rather 

 earlier stage. P. Levieri resembles P. radiculosa in the size and form of 

 the archegonium, but the involucre itself is more like that of P. Zollingeri. 



After fertilization the Qgg develops into the embryo, about which 

 is developed the calyptra, formed from the much enlarged venter of the 

 archegonium. The neck of the archegonium is carried up and forms a 

 slender process tipping the massive cylindrical calyptra. The latter is not 

 formed exclusively of the enlarged archegonium venter, but the adjacent 

 tissue also contributes to it. When complete the calyptra forms a sheath 



