86 



MOSSES AND FERNS 



CHAP. 



ened midrib, the outer cells dividing only by perpendicular 

 walls, forming the wings. From the ventral surface of the 

 young midrib papillae project, which curve up over the grow- 

 ing point, in the form of short two-celled hairs, whose end 

 cells secrete mucilage for its protection. In Aneura the growth 

 is very similar, but all of the cells divide by walls parallel to 

 the surface of the thallus, and no midrib is formed, and the 

 thallus is several cells thick in all parts. In both genera numer- 

 ous delicate colourless rhizoids are developed from the ven- 

 tral surface, especially of the midrib, when that is present. 



Aneura is of interest as showing the only case among the 

 Bryophytes of structures that may be compaied to the ZOO- 



B, Hymenophyton Aabeliatum, Xi^>; sp., young 



FIG. 38. A, Symphyogyna sp.; 

 sporophyte; b, young shoot. 



spores of the Green Algae. In A. multifida Goebel ((8), p. 

 337), discovered that the two-celled gemmae which had been 

 described as formed simply by a separation of the cells of the 

 thallus, were really formed within the cells and expelled from 

 them through an opening, after which they divided into two 

 cells and ultimately developed a young plant, much as an ordi- 

 nary spore would do. The absence of cilia from these cells, 

 which probably are the last reminiscences of the ciliated go- 

 nidia of the aquatic ancestral forms, is to be accounted for by 

 the terrestrial habit of Aneura. 



The branching is dichotomous, and is brought about by 



