46 THE MORPHOLOGY OF PTERIDOPHYTES 



periclinal divisions to give a long protruding neck, composed 

 of as many as six tiers of four cells. The central cell, mean- 

 time, divides to produce a 'primary ventral cell' and a 

 'primary neck canal cell' (Fig. 7F). Beyond this stage 

 there are several possible variants, only one of which is 

 illustrated in Fig. 7G, where the primary ventral cell has 

 divided to give an egg cell and a ventral canal cell, while 

 the nucleus of the primary neck canal cell has divided 

 without any cross wall being laid down. In the mature 

 archegonium, however, most of the cells break down so as 

 to provide access to the egg cell from the exterior, through a 

 narrow channel between the few remaining basal cells of the 

 neck, whose walls, in the meantime, have become cutinized 

 (Fig. 7H). 



The antheridium, likewise, starts with a perichnal division 

 in an epidermal cell (Fig. 7I). The outer cell is the 'jacket 

 initial' whose further divisions in an anticlinal direction give 

 rise to the single-layered antheridial wall, while the inner 

 'primary spermatogenous cell' gives rise to the spermato- 

 genous tissue, by means of divisions in many planes (Fig. 

 7L). At maturity (Fig. 7M) the antheridium is spherical, 

 projects from the surface of the prothallus and contains 

 numerous spirally coiled multiflagellate antherozoids (Fig. 

 7S). These escape into the surrounding film of moisture and, 

 attracted presumably by some chemical substance, find their 

 way by swimming to the archegonia, where fertilization 

 occurs. 



Stages in the development of the young sporophyte from 

 the fertihzed egg are illustrated in Figs. 7N-R. The first 

 division of the zygote is in a plane at right angles to the axis 

 of the archegonium (Fig. 7O) giving rise to an outer 'epibasal 

 cell' and an inner 'hypobasal cell'. The latter divides re- 

 peatedly to give a lobed attachment organ called a 'foot' 

 (Fig. 7Q), while the epibasal cell, by repeated divisions, 

 gives rise to the first rhizome, from which other rhizomes 

 and aerial shoots are produced. Fig. 7R shows a young 



