PTERIDOPHYTA— FILICIN^ 



137 



The cushion is formed by the cells in the middle line in the 

 anterior region then dividing in a plane parallel to the surface 

 so that the mass becomes several cells in thickness there. This 

 cushion bears the archegonia and may in a way be compared to 

 the archegoniophore of the liverworts. The antheridia do not 

 arise on the cushion, but towards the posterior margin. 



The antheridium is always superficial in origin {fig. 896). 

 An epidermal cell grows out and is divided into two, the 

 upper one of which produces the organ. 

 It divides into two cells, the lower of Pi^. 895, 



which forms a stalk-cell. The upper one 

 divides repeatedly, so as to form a wall 

 surrounding a central cell, in which the W*^ — 



mother cells of the antherozoids are pro- 27 



duced by repeated cell-divisions. In each 

 mother cell a single antherozoid is pro- 

 duced, which is a coiled filament furnished L . -^^ J /^ 

 with cilia at its anterior end {fig. 860, b). l!^' T A^^C^ 

 When the antheridium is mature it ^>^^ ^<^x^^^L\, 

 ruptures, and the mother cells, containing 

 the antherozoids, escape, the antherozoids 

 being liberated a little later. The whole 

 of the protoplasm of the mother cell is 

 not used up to form the antherozoid, so 

 that when the latter escapes it has usually' 

 attached to it a vesicle of protoplasm, the 

 rest of the contents of the mother cell. 



The development of the archegonium i^- -^ 



{fig. 897) is also from a superficial cell of 

 the prothallium, which segments into two, C-^'^^^' 

 an upper and a lower. The neck is de- _ '" 



rived from the former hy a succession ftages' in tiie eariy^^dl- 

 of divisions. It is much like the neck veiopment of the pro- 



« ,1 1 . /• xi ^ 1 thallus (gametophyte) of 



of the archegonmm OI the moss, but the Fern. After Kny. 



much shorter, consisting of only a few 



tiers of cells. The lower cell grows upwards into the neck, 

 separating its cells somewhat and forming the neck-canal-cell, 

 which remains smgle. The neck-canal-cell is cut off from 

 the remainder, which then constitutes the central cell of the 

 archegonium. This next cuts off a small ventral-ca^ial-cell, and 

 the remainder rounds itself off into an ovoid mass of protoplasm, 

 which is the oosjiliere. 



Later the ventral-canal-cell and the neck-canal-cell become 



