170 



BOTANICAL GAZETTE 



[SEPTEMBER 



spermatogenesis cell (figs. 20, 22). When only a single primary 

 prothallial cell is cut off, it may (fig. 19) or may not (fig. 21) divide 

 again. Far more frequently it does divide anticlinally. No case 

 in either species has been observed where either prothallial cell divides 

 periclinally. In case two prothallial cells are cut off, both usually 

 divide anticlinally (figs. 23, 26, 27), although the division may be long 

 delayed or fail wholly (text fig. 4) . The first one may remain undivided, 

 or in rare cases may divide twice, so that the first tier of prothallial 



Fig. i. Transverse section of a male gametophyte consisting of one prothallial 

 cell (pi), the primary spermatogenous cell (ps), and the tube nucleus (t). — Fig. 2. 

 Male gametophyte in which the primary spermatogenous cell has divided into the body 

 cell (be) and the stalk cell (sc), and in which all the gametophytic walls have broken 

 down. — Fig. 3. Same as the preceding except that there are four prothallial nuclei 

 instead of one; it is uncertain whether they have been derived from one or two primary 

 prothallial cells. — Fig. 4. A gametophyte with two primary prothallial cells (p If p 3 ) 

 which have not divided, though the pollen is presumably ready for shedding. — Fig. 5. 

 A gametophyte with a large stalk cell placed transversely to the axis of the body 

 cell. — Fig. 6. Same as preceding except that there are four derivatives of the primary 

 prothallial cell. — FlG. 7. A gametophyte in which the origin of the free nuclei is not 

 easily traced; see text for discussion. 



cells contains four cells. The second one almost always divides once 

 and usually twice. Thus there may be one, three, four, six, or eight 

 prothallial cells ; six is much the commonest number, and one or eight 

 the rarest. In case only one prothallial cell is cut off, its nucleus 



