Development of Sporangia upon Fern Prothalli. 253 



band, resembling a rudimentary vascular bundle, and suggesting a 

 comparison with the vascular supply of a sorus. 



The development of the sporangium could not be followed in 

 detail in the material obtained as yet, but a sufficient number of 

 stages have been found to make it clear that there is no difference of 

 importance from the well known course of development of thd same 

 member on the sporophyte. In the youngest stage seen the apex 

 of the sporangium was occupied by a tetrahedral cell, the cells 

 destined to form the lateral portions of the wall having already 

 been cut off from a large, dome-shaped terminal cell, the limits 

 of which were clearly recognisable. This was borne upon a stalk 

 cell. A tetrahedral archesporium is formed, from which tapetal 

 cells are cut off. The tapetum subsequently becomes two-layered, 

 and the central cell developes into a group of sporogenous cells. 

 From these, in the most mature sporangia found, a number of dark 

 brown spores had developed, while the tapetum was represented by 

 numerous granules between the spores. The number of spores 

 appeared to be the same as was contained in a sporangium developed 

 on the sporophyte. The sporangium wall was perfectly developed ; 

 the cells of the annulus showed the characteristic thickening of their 

 walls, which were of a dark brown colour, and a well formed stomium 

 was present. When tested with dehydrating agents, the mechanism of 

 the annulus was found to be perfect. The stalk consisted of four rows 

 of cells. 



JSTo sporangia have been found in which the spores were ripe, but in 

 .view of the advanced stage of development in those observed, there is 

 every probability that some may be obtained. It will be interesting 

 to ascertain if the spores are capable of germination, and if the 

 prothalli produced show any peculiarities. The spores seen already 

 possessed a thick wall on which indications of sculpturing were appa- 

 rent, and a single nucleus was present in each. 



When the unnatural conditions under which they developed are 

 borne in mind, it is not surprising that many imperfect sporangia 

 were found. Such sporangia were in fact the more numerous. Some- 

 times the arrest of development had taken place before the tapetum 

 had originated from the archesporium, but more commonly the double 

 layer of tapetal cells was present surrounding a sporogenous cell 

 which had become highly refractive, the nucleus being indistinguish- 

 able. The annulus could be made out, but its cells were thin walled 

 and colourless, and the whole sporangium was pale and more flattened 

 than one of the same age in which sporogenous tissue had formed. 



No evidence has yet been obtained of the production of sporo- 

 phytes, showing vegetative organs upon the cylindrical process, but 

 one example was seen in which a group of sporangia, situated on the 

 apex of the process, was surrounded by ramenta. 



VOL. LX. u 



