PTERIDOPHYTA— PILICINiE 



137 



the 



Fig. 895. 



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 anthcridium is always superficial in origin {fig. 

 All epidermal cell grows out and is divided into two 

 upper one of which produces the organ. 

 It divides into two cells, the lower of 

 which forms a stalk-cell. The upper one 

 divides repeatedly, so as to form a wall 

 surrounding a central cell, in which the 

 mother cells of the antherozoids are pro- 

 duced by repeated cell-divisions. In each 

 mother cell a single antherozoid is pro- 

 duced, which is a coiled filament furnished 

 with cilia at its anterior end {fig. 860, b). 

 When the antheridium is mature it 

 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 arohegonium 

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

 the prothallium, which segments into two, 

 an upper and a lower. The neck is de- 

 rived from the former by a succession 

 of divisions. It is much like the neck 

 of the arohegonium of the moss, but 

 much shorter, consisting of only a few 

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

 separating its ceUs somewhat and forming the neck-eanal-ceU, 

 which remains single. The neck-oanal-oeU is cut off from 

 the remainder, which then constitutes the central cell of the 

 arohegonium. This next outs off a small ventral-canal-cell, and 

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

 which is the oosphere. 



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



Fi^ 895 1-5 Successive 

 stages in the early de- 

 velopment of the pro- 

 thallus (gametophyte) of 

 the Fern. After Kny. 



