XI LEPTOSPORANGIATAi HETEROSPORE^ 403 



thallium (Fig. 235, A). This nucleated protoplasm is free 

 from the large albuminous granules in the lower part of the 

 spore cavity, and in stained sections presents a finely granular 

 appearance, and is evidently concerned with the elaboration of 

 the reserve food materials in the large spore cavity. In ex- 

 ceptional cases indications of the formation of cell walls be- 

 tween these nuclei were seen, but usually they remained quite 

 free. Whether a similar state of affairs exists in Salviiiia re- 

 mains to be seen. 



When the first archegonium is ripe, the prothallium is nearly 

 hemispherical, with the originally convex base strongly concave. 

 The central cell of the archegonium is separated by one, some- 

 times two, layers of cells from the spore cavity, and the neck 

 projects considerably above the surface of the prothallium. 

 The latter now pushes up between the softened episporic mass 

 at the top of the spore, and the archegonium is exposed. In 

 cross-section the prothallium is more or less triangular (Fig. 

 235, E), with one angle longer than the others. This longer 

 arm corresponds to the "sterile third" of the prothallium of 

 Salvinia, and represents the first cell cut off from the prothallium 

 mother cell. 



If the first archegonium is fertilised, no others are formed; 

 but usually several secondary ones are present. The second 

 archegonium arises close to the primary one; indeed its cen- 

 tral cell is generally separated from it only by a single layer of 

 cells. The third arises near the base of the larger lobe (Fig. 

 235, E). In case all of these prove abortive, others develop 

 between them apparently in no definite order, and to the num- 

 ber of ten or occasionally more. In the older prothallia these 

 later archegonia are sometimes borne in small groups upon ele- 

 vations between the older ones. 



The neck canal cell of the archegonium is formed much 

 earlier than Pringsheim describees in Salvinia, and is cut off 

 from the central cell about the time the first divisions take 

 place in the cover cell. Each row of the neck has four cells, 

 as in Salvinia, and the neck canal cell may have its nucleus 

 divide, as in Isoetes and the homosporous Filicineae. This has 

 not yet been observed in Salvinia. 



In Salvinia (Pringsheim (i), Prantl (4)) the prothallium 

 is large and develops a good deal of chlorophyll. It has a very 

 characteristic appearance, and shows the same triangular form 



