84 



MOSSES AND FERNS 



CHAP. 



dorsal lamina or wing, which may be more or less spirally 

 placed, owing to torsion of the axis, but this torsion was much 

 exaggerated in the early figures of the original species, R. 

 helicophylla. According to Goebel's investigations, the grow- 

 ing point is formed secondarily, and this statement is con- 

 firmed by Howe's studies. The latter writer has studied the 

 germination of the spores and has described the formation of 

 gemmae in R. Americana. 



The latest contribution to our knowledge of Riella is that 

 of Porsild (i). He confirms Howe's statements and has 



Fig. 36.— a, D, Riella Americana; B, C, R. helicophylla; A, Apex of female plant, X8; 

 B, C, lateral and ventral view of the growing point, X500; x, apical cell ;£., leaves. 

 D, male plant, XiH; fA, D, after Howe ; B, C, after Leitgeb.) 



further investigated the question of the growing point. He 

 finds that while an apical cell is absent in the younger stages, 

 it is formed later in normal plants. 



Both archegonia and antheridia resemble those of Sphcero- 

 carpus very closely, and the structure of the sporophyte is also 

 the same, no true elaters being developed, but instead there 

 are simply sterile cells. 



