424 



MOSSES AND FERNS 



CHAP. 



radiae arrangement, extending in lines from the nucleus to the 

 periphery. The first division may occur before the spore has 

 changed form, and in this case (Fig. 218, 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 conditions, 

 this may reach a length considerably exceeding the diameter 



Fig. 219. — Young prothallia of Egtcisetum, showing the variation in form, X i8o. In A there is 



apparently a definite initial cell ; r, rhizoid. 



of the spore. Sadebeck ^ showed and Buchtien " confirmed 

 this, that the first root-hair is positively heliotropic. 



The first divisions in the prothallial cell are extremely 

 various, in this recalling the behaviour of the eusporangiate 

 Filicineae and the Osmundaceae. The first wall may be either 

 vertical or transverse (Fig. 2 1 8), 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 

 repeated transverse divisions, form two parallel rows of cells, 

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



^ Sadebeck (6), p. 177. - Buchtien (i), p. 29. 



