xii EQUISETINEsE 445 



changed form, and in this case (Fig. 257, C) a small cell is cut 

 off by a strongly curved wall. Both cells contain chlorophyll, 

 but the nucleus of the smaller cell is smaller than the other. 

 In other spores there is first an elongation, as in Osmunda, and 

 the smaller end, which like that has some chlorophyll, but not 

 so much relatively as the larger, is cut off, and forms the first 

 rhizoid, and within twenty-four hours, under suitable condi- 

 tions, this may reach a length considerably exceeding the diame- 

 ter of the spore. Sadebeck ( (6), p. 177) showed and Buchtien 



FIG. 258. Young protTiaflia of Equisetum, showing the variation in form, Xi8o. In A 

 there is apparently a definite initial cell; r, rhizoid. 



((i), p. 29) confirmed this, that the first rhizoid is positively 

 heliotropic. 



The first divisions in the prothallial cell are extremely vari- 

 ous, in this recalling the behaviour of the eusporangiate Fili- 

 cineae and the Osmundaceae. The first wall may be either ver* 

 tical or transverse (Fig. 257), and sometimes, but not often, 

 there are several transverse walls, and a short filament is 

 formed. More commonly the first transverse wall is followed 

 by a vertical wall in one or both cells. In case the first wall is 

 vertical it not infrequently happens that the two cells, by re- 

 peated transverse divisions, form two parallel rows of cells, 

 which may diverge, so that the young prothallium becomes two- 

 lobed. In a number of cases a two-sided apical cell was seen 

 (Fig. 258), but its growth is very limited. Finally, a cell-mass 



