Page:Proceedings of the Royal Society of London Vol 60.djvu/279

Rh band, resem bling a rudim entai’y 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 m aterial obtained as yet, b u t a sufficient num ber of stages have been found to m ake it clear th at there is no difference of im portance from the well known course of developm ent of the same member on the sporophyte. In th e youngest stage seen the apex of the sporangium was occupied by a tetrah ed ral cell, the cells destined to form the lateral portions of the wall having already been cut -off from a large, dome-shaped term inal cell, the lim its 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 ceutral cell developes into a group of sporogenous cells. From these, in the most m ature sporangia found, a num ber of dark brown spores had developed, while the tapetum was represented by numerous granules between the spores. The num ber 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 th eir walls, which were of a dark brown colour, and a well formed stom ium was present. When tested w ith dehydrating agents, the mechanism of the annulus was found to be perfect. The stalk consisted of four rows of cells.

No 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 th at some may be obtained. I t will be interesting to ascertain if the spores are capable of germ ination, and if the prothalli produced show any peculiarities. The spores seen already possessed a thick wall on which indications of sculpturing were- apparent, and a single nucleus was present in each.

When the unnatural conditions under which they developed are borne in mind, it is not surprising th at many im perfect sporangia were found. Such sporangia were in fact the more numerous. Sometimes the arrest of development had taken place before the tapetum had originated from the archesporium, but more commonly the double layer of tapetal cells wTas present surrounding a sporogenous cell which had become highly refractive, the nucleus being indistinguishable. 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 sporophytes, 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.