228 On Azolla and Salvinia. 



The fourth stage presented them as still more oblong, with 

 a tendency to an urceolar form. The once protruding nuc- 

 leus is now completely concealed, the cup having become ex- 

 tended beyond its apex into a short mammilla having a narrow 

 orifice (the foramen). Minute examination at this stage dis- 

 closes a tendency, at least in appearance, in the aforesaid 

 mammilla to be lobed, as though it had been produced, not 

 by one, but by about four component parts. The same 

 stage has generally presented moniliform filaments in apposi- 

 tion with the apex of one or both organs. (PL 15./. 5.) These 

 moniliform filaments are found within the involucrum from the 

 earliest period examined, but were not observed to have any 

 positive relations with the organs before this period. They 

 now plainly pass into the organs, and have therein sooner 

 or later appeared to be resolved into their component 

 joints, which occupy the cavity existing between the once 

 protruding body and the foramen. (PL 15. f. 7. 8. 10. 11.) 

 And this is so constant, that even in cases where the 

 moniliform filaments are not seen in application with the 

 foramen, or passing through it, the space just particularised 

 will be found filled with their component parts. (PL 15. f. 

 \2. 13. 14. 15.) 



Up to this time both the organs have presented a cellular 

 surface of the usual colour ; each cell of the surface con- 

 taining a nucleus, likewise of the ordinary herbaceous colour. 



The fifth stage presents the base of the nucleus surround- 

 ed by small cellular protuberances. (PL 15. f. 12. 13. 14.) 

 The moniliform filaments are the same. The cells of the 

 surface of each organ are more developed, and have begun 

 to assume a rosy tint. The nuclei of these cells also are not 

 only more distinctly defined, but are in most cases of a pink 

 tint, in some deep pink. 



Throughout these stages small cellular protuberances have 

 been developing from the axis outside the base of either or- 

 gan. These at the stage under consideration are simple, 



