PTEROPSIDA 



173 



later ones microsporangia, in large numbers, on branched 

 stalks (Fig. 27I). All except one of the potential megaspores 

 in each megasporangium abort, and the functional mega- 

 spore becomes surrounded by a thick perispore (Fig. 27J), 

 which later becomes cellular and comes to look, super- 

 ficially, like the pollen chamber of a gymnosperm seed. 



Fig. 27 



Azolla: a, portion of plant of A. filiculoides; b, sporocarp with 

 young megasporangium; c, megasporangium with massulae; 

 D, the same with female prothallus; e, massula from micros- 

 porangium; f, male prothallus. Salvinia: g, portion of plant of 

 S. natans; h, node with sporocarps; i, sporocarps with mega- 

 sporangia and microsporangia; J, megasporangium; k, micro- 

 sporangium; L, male prothallus; m, archegonium; n, female 

 prothallus with young sporeling attached 



(1, column; 2, leaf; 3, root) 



(b, after Pfeififer; c, e, Bernard; d, Campbell; f, l, Belajeff; 

 G, H, Bischoff; i, Luerssen; J, Weymar; k, h, Yasui; n, Lasser) 



