Page:Proceedings of the Royal Society of London Vol 60.djvu/277

Rh a m ixture of vegetable m ould and sand. The pot was kept constantly covered with a glass plate, and the necessity of w atering was avoided by standing th e pot in a large saucer kept full of w ater. A close crop of well-formed prothalli, on w hich antheridia and archegonia were present, com pletely covered the surface of th e soil. In April, 1896, a num ber of th e prothalli bore norm al embryos in an early stage of developm ent. Three m onths later num erous young plants were present, w hich were found on exam ination to be normally produced.

The prothalli which had not been fertilised had lost the heartshaped outline and elongated considerably ; some of them reached a length of 2 cm., and were 5 mm. in breadth. The archegonia were very numerous, and were situated upon a distinct cushion, which was continued in the larger p ro th alli as a w ell-m arked m idrib. They were arranged in transverse rows ; th eir necks had opened in a normal m anner, and th e canal showed the usual brow n discoloration. Antheridia were present on some of the prothalli.

In some of these prothalli the m idrib was continued into a cylindrical process of variable thickness. This arose in some examples as a direct continuation of the apex, b u t more frequently was attached to the under surface, ju st behind the apex of the prothallus ; in one instance it was found in a corresponding position on th e upper su rface. The actual apex usually loses its m eristem atic appearance ; it grows out as a narrow trian g u lar lobe, w hich consists of colourless cells, and contains tracheides. This lobe closely resembles the “ middle lobe ”* found in the apogamous prothalli of certain ferns, and probably corresponds to it. In a few instances this m iddle lobe is formed, but no cylindrical process arises ; in such cases secondary prothalli are produced from th e anterior m argin of the thin lateral wings, and the whole closely resembles an aborting prothallus of Aspidium filx-masor Pteris cretica. W hen the prothalli are seen from above, the anterior edge can be traced across the base of the cylindrical process. As will be described below, the first sporangia formed on the prothallus are usually situated on this m argin, especially on the “ middle lobe.” The process is of the same deep green colour as the midrib. Sexual organs, often in considerable numbers, are borne upon it. They are usually well form ed; the archegonia open in the usual manner, and the spermatozoids are capable of active movement when liberated. On other examples variously malformed sexual organs occur. The abnormal archegonia are seated upon small elevations composed of cells which contain chlorophyll ; sometimes the neck is open, but other examples have the

1878, p. 463.
 * Farlow, 4 Quart. Journ. Microscop. Sc.,’ 1874, p. 268. De Barv, ‘ Bot. Zeit.,’