Dr. E. Strasburger on Fertilization in Ferns. 333 



becomes so large as to hamper its movements and prevent its 

 advancing ; such spermatozoids may be seen, when the period 

 of their swarming is nearly over, sinking to the bottom, where 

 the vesicle and finally the spermatozoid are absorbed. 



Before proceeding to relate the behaviour of the spermato- 

 zoids, Dr. Strasbm-ger thus describes the development of the 

 archegonia : — 



Certain cells on the underside of an old prothallium, just 

 behind the indentation of the front margin, and where it has 

 attained some thickness, become the mother cells of archegonia. 

 One of these cells is first divided, in a direction parallel to the 

 surface of the prothallium, into an inner and larger cell, which 

 becomes the central cell of the archegonium, and an outer, 

 rather smaller one, which, after repeated division, forms the 

 neck of the archegonium ; by subsequent divisions the mother 

 cell acquires two or more layers of cells. The canal through 

 the neck is formed by the retreat of its central layer of cells 

 from their contact with each other, or by absorption, where a 

 central layer exists. But previously to this a delicate spherical 

 cell is formed around the nucleus of the central cell, which 

 becomes the mother cell of the future plant. A mass of proto- 

 plasm is then collected around the nucleus of the central cell, 

 the protoplasm is separated from the other contents of the 

 central cell by a convex line of demarcation, and thus becomes 

 an independent cell ; but no membrane composed of cellulose 

 is demonstrable. The cell formed within the central cell is 

 not the germ-vesicle, but rather the canal-cell, as Pringsheim 

 has shown in Salvinia. The remaining contents of the cen- 

 tral cell constitute the future germ-sphere ; in its midst, close 

 beneath the canal-cell, there lies a large nucleus with a dis- 

 tinct nucleolus. After further divisions of the neck-cells, the 

 canal-cell pushes itself between them, and carries them up 

 with it ; within this cell a number of nuclei may now be seen. 

 The growth of the cells of the neck does not proceed equally 

 on all sides, so that the neck is bent down, and its crown cell 

 turned towards the prothallium. When the number of the 

 neck-cells is complete, another scries of divisions takes place 

 in the cells surrounding the central cell ; at the same time the 

 nuclei of the canal-cells resolve themselves slowly into a num- 

 ber of little granules, and unite at length into a granular mass, 

 which soon fills the whole canal. The lower neck-cells now 

 enlarge, thereby diminishing that portion of the canal ; and its 

 granular contents are thus partially forced into the upper ])art, 

 there forming a wedge-shaped mass, which connects itself by 

 a frequently very slender thread with that occujiying the cen- 

 tral cell, if the archegonium be now brought into contact 



