562 THE GAMETOPHYTE OF PSILOTUM, 



dome-like in shape, and of a slight brown tint. Very many 

 examples have been seen, in sitx, in all stages of development. 

 Each female spore produces one gametophyte; in no instance 

 have two been observed. During my investigations, upwards of 

 one hundred slides have been mounted in glycerine-jelly, and only 

 about six show the gametophyte in situ. 



The evidence that this dome-shaped structure is the full-grown 

 prothallus, is now definitely established. Within the last fort- 

 night, fex-tilised archegonia, and embryos filling the cavity of the 

 dome, have been found on many slides; and one, in particular, 

 lias at least a dozen embryos, some visible through the wall of 

 the dome, and also through the ringed aperture at the base. 

 There are also some in which the wall of the dome has been 

 broken away, and the outlines and cell-structure can be seen. In 

 one instance, the embryo is quite free, and exhibits certain in- 

 dications of the division into regions such as are exhibited in the 

 early stages of Archegoniates generally. 



The female gametophyte appears to reach maturity when it 

 lias attained to a diameter of about 0-035 or 0*04 mm. On 

 opposite sides of the dome, near the summit, and in a line with 

 the longer axis of the spore, two clusters of cells ma}^ be observed. 

 These are transparent, and subtend the aperture in the neck of 

 the archegonia. Each cluster appears to consist of four cells, 

 two of which are more elevated than their fellows. The rest of 

 the archegonium is imbedded in the wall of the dome. In two 

 instances, archegonia have been observed only partly imbedded, 

 more than half being visible. If fertihsation takes place, the 

 whole structure rapidly increases in size generally, and some of 

 the brown cells on the ring and on other parts of the dome 

 become enlarged, and often develop into rhizoids. The inner, 

 cellular portion of the dome appears to be absorbed to furnish 

 nutrition foi- the growing embryo. The wall becomes thin, and, 

 when fractured, Ineaks with an angular appearance like broken 

 glass. As growth proceeds, the rhizoids increase in size, and it 

 seems possible that they may be functional all the time, either as 

 simple cells or when elongate. 



