THE HIGHER CRYPTOGAMIA. 185 



of the cells of their outer edge (PI. XXIV, fig. G). The 

 apical cell for the time being of the wing of the prothallium, 



is continually pushed downwards and outwards and re- 

 placed by a younger one. The growth of the youngest 

 cells in the direction diverging from the longitudinal axis 

 of the side wings is frequently more active at their inner 

 than at their outer end. AVhere this phenomenon is very 

 strongly manifested it leads to such a remarkable develop- 

 ment of the breadth of the two wings of the prothallium 

 that the one overlaps the other. This circumstance how- 

 ever occurs, for the most part at least, only in prothallia of 

 exuberant growth ; it does not take place until the termina- 

 tion of the normal growth of the prothallium. 



Individual cells of the under side of the prothallium pro- 

 trude outwardly in a hemispherical form. In very young 

 prothallia, or in thin shoots of old exuberant prothallia, the 

 same thing occurs in the marginal cells (PI. XXIV, fig. 4). 

 The development of these cellular excrescences usually 

 commences at the hinder part of the prothallium, proceed- 

 ing from thence towards the front part, but without any 

 very great regularity. As a rule one excrescence only is 

 developed on one cell of the prothallium. In the median 

 line of the latter, one of these excrescences is produced from 

 almost every cell ; towards the sides their number dimin- 

 ishes, and at the edges of the wings of the prothallia the 

 formation is entirely suppressed. Their expansion coincides 

 with that of the radicular appendages. The protruding 

 portion of the free outer surface of the cell is soon separated 

 from the primary cell-cavity by a transverse septum. This 

 transverse division is often repeated a second time, more 

 rarely several times, so that the hemispherical terminal cell 

 of the excrescence is supported by one, or by several, discoid 

 shortly cylindrical cells. The nature of their contents 

 differs little at first from that of the vegetative cells of the 

 prothallium. The walls are covered by a layer of chloro- 

 phyll having somewhat smaller granules than that of the 

 neighbouring cells ; their supply of protoplasm is somewhat 

 larger. Prom this period the highly refractive protoplasm 

 of the young antheridium accumulates to such an extent, 

 that the arrangement of its component cells is very difficult 



