308. On Isoetes lacustris, Linn. \ Jan. 31, 



the spore into an apical and a basal portion, and while the latter 

 for some time undergoes no further change, the apical cell is divided 

 very rapidly into a number of cells, whose arrangement can still be 

 followed even in quite old prothallia. When the first primary cells 

 are formed, the nuclei are again distinguishable on staining with 

 hsematoxylin, but they are of exceedingly small dimensions, and with 

 this change the staining capacity of the protoplasm becomes less 

 marked. Divisions in all planes proceed very rapidly in the upper 

 (apical) portion of the prothallium, and the rudiments of the arche- 

 gonia are laid down much as in the Marat tiaceEe. Periclinal division 

 of single superficial cells into two takes place, the upper of which 

 gives rise to the neck, and by repeated division forms four stories, each 

 story being again divided crosswise into four cells arranged as quad- 

 rants of a cylinder. The lower cells form the central series, in which 

 a neck canal cell is cut off, and then a ventral canal cell, from the 

 oosphere. The canal cells then thrust themselves between the neck 

 cells, and cause a distortion in the two lower stories, which may be so 

 great as even to render them difficult of recognition. 



Whilst these changes have been taking place in the upper (apical) 

 of the two primary cells, the lower (basal) one is dividing, but com- 

 paratively slowly, and it is easily distinguishable in that the cells 

 arising from it remain of a large size as compared with those formed 

 in the upper part of the prothallium. In spite of repeated search 

 through a great number of preparations, it has not been found possible 

 hitherto to arrive at a satisfactory conclusion as to the mode of cell- 

 division which prevails in the secondary stage, for no karyokinetic 

 figures could be detected ; nevertheless, it is highly probable that the 

 process does not differ in any important respect from that exhibited 

 by other plants, and the arrangement of the nuclei about the walls of 

 recently formed cells makes this supposition almost a certainty. 



I have purposely omitted any reference to the researches of other 

 observers in the present paper, and it was not my object to attempt a 

 complete account of my own work, which is still in progress, but the 

 results detailed above appeared of sufficient interest to justify the 

 appearance of this note. 



