558 THE GAMETOPHYTE OF PSILOTUM, 



The re-examination of all the material at my disposal tended 

 to support the opinion that the dome-shaped structure may be 

 the fully-formed female gametophyre. During the re-examina- 

 tion, upwards of 100 specimens of this dome-shaped structure, in 

 all stages of development, were carefully studied. The most 

 sti'iking features noted were the uniformity as to structure and 

 dimensions; and the great variabilit}' in tlie colour of the dome- 

 shaped structure, according to age. In the young form, it is 

 fairly transpai-ent, but, M'hen it reaches maturity, it assumes a 

 slightl}' brownish tint, with the exception of the projecting cells, 

 which remain clear and are visible through the ringed aperture, 

 with their bases imbedded in the wall of the upper part of the 

 dome. tSome of these projecting cells appear to be flask-shaped, 

 but they are too much imbedded for the details to be cleai-ly 

 seen. T assume that these projecting cells are the archegonia. 



When the dome has attained a diameter of 0'05 mm., it ceases 

 to increase in size, and gradually becomes darker in coloui', — the 

 rusty-brown colour always developed in the unfertilised arclie- 

 gonia of ferns. 



On one of the slides examined, there were several examples of 

 these domes, measuring about 0*08 mm., and these were fairly 

 ti'an.sparent, except the ring, which was deeply coloured, and 

 stood out very distinctly. The hollow of the dome appeared to 

 be filled up; and, in some cases, there was an appearance of 

 bulging at the opening, — perhaps showing that fertilisation had 

 taken place. 



The pavement-like character of the cell-structure (the cells 

 being imbedded in gum) allows of expansion, within certain 

 limits, to accommodate the growth of the embryo. The ring- 

 may be regarded as a ready means of separation from the spore, 

 the dome being left as a protecting cap on the broad end of the 

 embryo, until further growth renders it unnecessary. 



On the slide referred to above, there wei^e several peculiar 

 bodies which may be said to reach the climax of the puzzles 

 connected with the study of the gametophyte of Psilotum. The 

 first specimen seen was wedge-shaped, the broad end of the wedge 



