Development of Sporangia upon Fern Prothalli . 251 



a mixture of vegetable mould and sand. The pot was kept con- 

 stantly covered with a glass plate, and the necessity of watering 

 was avoided by standing the pot in a large saucer kept full of water. 

 A close crop of well-formed prothalli, on which antheridia and arche- 

 gonia were present, completely covered the surface of the soil. In 

 April, 1896, a number of the prothalli bore normal embryos in an 

 early stage of development. Three months later numerous young 

 plants were present, which were found on examination to be nor- 

 mally produced. 



The prothalli which had not been fertilised had lost the heart- 

 shaped 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 prothalli as a well-marked midrib. They 

 were arranged in transverse rows ; their necks had opened in a 

 normal manner, and the canal showed the usual brown discoloration. 

 Antheridia were present on some of the prothalli. 



In some of these prothalli the midrib was continued into a cylin- 

 drical process of variable thickness. This arose in some examples as 

 a direct continuation of the apex, but more frequently was attached 

 to the under surface, just behind the apex of the prothallus ; in one 

 instance it was found in a corresponding position on the upper sur- 

 face. The actual apex usually loses its meristematic appearance ; it 

 grows out as a narrow triangular lobe, which 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 middle 

 lobe is formed, but no cylindrical process arises ; in such cases 

 secondary prothalli are produced from the anterior margin of the 

 thin lateral wings, and the whole closely resembles an aborting pro- 

 thallus of Aspidium filix-mas or Pteris cretica. When 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 spo- 

 rangia formed on the prothallus are usually situated on this margin, 

 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 formed; 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 chloro- 

 phyll ; sometimes the neck is open, but other examples have the 



* Farlow, ' Quart. Journ. Microscop. Sc.,' 1874, p. 268. De Baiy, ' Bot. Zeit./ 

 1878, p. 463. 



