35 6 



PART IV. VEGETABLE TAXONOMY. 



very rudimentary prothallium. The female prothallium is better 

 developed, consisting of a mass of cells, but it projects but little 

 from the spore. The plants are rootless, floating aquatics, hav- 

 ing flat aerial leaves, and finely dissected, submerged ones. The 

 sori are rounded bodies com- 

 pletely enclosed in an indusium, 

 and borne near the base of the 

 submerged leaves. See Fig. 

 563- 



Fig. 564. 



Fig. 563. — Salvinia natans. A, portion of plant showing aerial leaves, a, submerged 

 leaves, b, and sori s, borne on the submerged leaves. B, a cluster of the sori in section, 

 magnified about to diameters «. a sorus containing macrosporangia, and m, m, sori con- 

 taining microsporangia. Partly after Sachs. 



Fig. 564. — Marsilea salvatrix. st, stem, bearing roots and leaves ; /, leaf petiole 

 giving off a fructifying branch ; f,f, fruits, containing sporangia which bear both macro- 

 spores and microspores. 



In the Marsilias the contents of the microspore in germinat- 

 ing also form three cells, two of which together make up the 

 antheridium, and the other, which is very small, stands for the 

 prothallium ; but they all remain enclosed within the spore until 

 the antherozoids are ripe. 



