VIII 



THE P TERIDOPH VTA — OPHIOGLOSSA CE^ 



'-2>7 



be traced to a single cell, as Goebel asserts is probably the case 

 in O. vulgatum. 



A transverse section of the very young sporangiophore is 

 somewhat triangular, the broader side corresponding to the 

 outer surface of the sporangiophore. The cells are very irre- 

 gular in form, and no differentiation of the tissues is to be 

 observed. Sections of somewhat older stages show in some 

 cases, at least, a large epidermal cell occupying nearly the 

 centre of the shorter sides of the triangular section. This cell 

 has a larger nucleus than its neighbours, and is decidedly broader. 



B, 



Fig. I20. — A, Very young ; B, older sporangia oi O. pendulwn ; transverse sections, X260. 



The next stage was not observed, but a somewhat more advanced 

 one shows a small group of inner cells (shaded in the figure), 

 which appear to have arisen from the primary cell by a trans- 

 verse wall, although this point is exceedingly difficult to deter- 

 mine on account of the great similarity of all the cells (Fig. 

 120). This group of inner cells (or the single one from which 

 they perhaps come) constitutes the archesporium, and b}' rapid 

 division in all directions forms a large mass of cells whose 

 contents become denser than those of the surrounding ones, 

 between which and these, however, the limits are not very plain. 

 Later, when the number of cells is complete, the difference 



