23 



observations to hand as yet wlietlier the shoots bearing 

 different reprodnctive organs are borne on the same root. 

 It is highly probable, however, that they are not. 



1. — The Xemathecium. 



The tetraspores are formed in great numbers in certain 

 younger portions of the frond. They make their 

 appearance during the winter months, probably from 

 December to March. AVhen held to the light slightly 

 oval but elongated dark spots may be seen near the apical 

 and younger portions of the frond. These darker portions 

 may be accompanied by a slight bulging out of the assimi- 

 lating layers, but this is never very marked. Each dark 

 part is a nemathecium, containing tetraspores (fig. 19). 



In a longitudinal or in a transverse section (fig. 20), 

 through a nemathecium the dark colour of the latter is 

 seen to be due to a dense and rather irregular mass of 

 small round cells. These may be the finished tetraspores, 

 or their mother-cells. Each mother-cell gives rise to four 

 tetraspores — hence their name. 



The whole internal tissue of the nemathecium consists 

 of irregular rows of cells, which on the one hand join on to 

 the collecting and a few of the conducting cells, and on 

 the other hand pass into the assimilating layers (fig. 21). 

 It is, however, before they enter the latter that their cells 

 swell up at the expense of the neighbouring cells, which 

 have a large store of starch. 



When these cells have attained a certain size they 

 divide into four cells each. They are, in fact, the tetra- 

 sporangia or mother-cells of the tetraspores (fig. 22). The 

 original cell-rows are at first easily made out (fig. 21), but 

 gradually the cells by their growth exert a certain amount 

 of pressure in all directions and the regularity of the cell 

 rows is disturbed. The surrounding sterile cells gradually 



