382 MOSSES AND FERNS chap. 



common with the true Filices, his figure of Azolla is extra- 

 ordinarily like the simple male prothallia that sometimes occur 

 among the Polypodiaceae. The small cell, cut off subsequently 

 from the basal cell, which he describes, I failed to find in any 

 of my sections, and the conclusion reached after careful study 

 was that but one vegetative cell (the large basal one) is formed, 

 and that the rest of the prothallium is to be regarded as a 

 single terminal antheridium. 



The subsequent divisions correspond to Belajeffs account. 

 In the middle cell of the antheridium two nearly vertical walls 

 are formed, which with the top cell (cover cell) completely 

 enclose the central one. The cover cell recalls in form and 

 position the same cell in the antheridium of the Polypodiaceae, 

 but is formed here previous to the separation of the central cell. 

 In one of the lateral cells a horizontal wall is formed, so that 

 the sperm cells are surrounded by five parietal ones. The 

 central cell now divides by a median vertical wall, and each of 

 the daughter cells twice more, so that eight sperm cells are 

 formed, as in Salvinia. The prothallium remains embedded in 

 the substance of the massula, and the spermatozoids probably 

 escape by the softening of the outer part of the latter. In 

 Salvinia the prothallia project beyond the sporangium wall, and 

 are easily separated. 



The antheridium of the Salviniaceae does not closely 

 resemble that of any other group. Azolla differs less from the 

 homosporous Ferns in this particular, and shows some resem- 

 blance to the Hymenophyllaceae in the arrangement of the 

 parietal cells. Occasionally a triangular opercular cell occurs 

 in Azolla, which recalls that in Osiminda. 



The Female Pi'otJialliuin 



The macrospores of Azolla filicidoides are borne singly in 

 the sporangia. The spores only germinate after they have 

 been set free by the decay of the indusium, the upper part of 

 which, however, persists as a sort of cap. The decay of the 

 sporangium wall and indusium exposes the curious . tuberculate 

 epispore, with its filamentous appendages, which serve to hold the 

 massulae, which are firmly anchored to them by their peculiar 

 hairs (glochidia) with their hooked tips. This is evidently of 

 advantage by bringing the male and female plants together. 



