PTERIDOPHYTA 



229 



and the inner one the 'primary ventral cell (Fig. 18oC). The primary neck 

 canal cell, by additional transverse divisions, gives rise to a variable num- 

 ber of neck canal cells, while the primary ventral cell, by a single transverse 

 division, produces the ventral canal cell and egg (Fig. \8oD-F). In some 

 species there are 4 to 6 neck canal cells. In Lycopodium cernuum the 

 number has been reduced to 1, while in Lycopodium complanatum as many 

 as 16 have been counted. The presence of numerous neck canal cells is a 

 primitive feature not seen in other living pteridophytes. 



Fig. 185. Archegonial development in Lycopodium clavatum, X 150. A, young arche- 

 gonium after first division of initial cell; B, vertical division of primary neck cell and trans- 

 verse division of inner cell to form basal cell and central cell (both shaded) ; C, division of 

 central cell to form primary neck canal cell and primary ventral cell; D, later stage, showing 

 basal cell, primary ventral cell, and four neck canal cells; E, nearly mature archegonium 

 with egg, ventral canal cell, and six neck canal cells; F, older stage, the canal cells breaking 

 down. (After Bruchmann.) 



Embryo. The fertilized egg divides transversely to form an outer sus- 

 pensor cell and an inner embryonal cell (Fig. 186A). The suspensor cell 

 may or may not divide again but usually elongates and pushes the embryo 

 a short distance into the prothallium. The embryonal cell, by two ver- 

 tical divisions at right angles to each other, gives rise to quadrants, each 

 of which then divides transversely to form eight cells in two tiers (Fig. 

 186B-^). Of these, the tier lying next to the suspensor develops the 

 foot, while the lower tier gives rise on one side to the stem and on the other 

 side to the leaf (Fig. 186i^-7). The foot is a temporary organ that 

 absorbs food from the gametophyte. It persists until the sporophyte has 

 become independent. The primary root is formed relatively late and 

 arises from the same tissue that produces the leaf. 



Summary. In Lycopodium an elongated, generally branched stem 

 bears numerous small leaves. In Phylloglossum a short tuberous stem 

 produces a few small leaves in a cluster. The vascular system of the stem 

 of Lycopodium is a protostele, fundamentally radial in organization, with 

 exarch development of xylem. Secondary thickening is absent. In the 



