433 Prof. II. Karsten on the Formation, 



uionia on the septum, when in course of thickening, and while 

 apparently still simple, the limits of the two daughter cells 

 forming it are distinctly seen ; in other words, its construction 

 out of two lamellae is demonstrated. Iodine, when applied in a 

 concentrated state, has a more energetic solvent action upon the 

 recently thickened primary cell-membrane ; and when its solu- 

 tion is diluted, it is at the same time exosmotic in its action on 

 the contents of the secondary cells. 



If these solvents be allowed to act for a time upon half- 

 lignified septa, the different component cell-membranes of which 

 have been separated from each other as much as possible by 

 means of diosmotic fluids, the newly lignified septum thus set 

 free is eroded at the centre, and finally more or less dissolved, 

 whilst the two contracted and mutually adherent daughter 

 cells float freely in the cavity of the parent cell. Examples 

 such as that represented in fig. 67, of a Spirogyra treated 

 with glycerine and afterwards with a solution of iodine, should 

 therefore be cautiously used in elucidation of the mode of origin 

 of a septum. 



In this experiment it now and then happens that one young 

 joint-cell (as shown in PI. VII. fig. 67) which is adherent by one 

 extremity to its neighbouring sister cell, and with it detached 

 on every side from the mother cell, is at the same time still 

 attached to the opposite end of its mother cell, by which a con- 

 siderable tension of the young cell in its long diameter is pro- 

 duced, and being transferred to the neighbouring septum, is 

 exerted chiefly on the delicate young wall in process of lignifica- 

 tion. This is consequently somewhat drawn into the cavity of 

 the extended cell until it becomes lacerated at its point of union 

 with it, whereupon it again assumes its flat form, and the second 

 daughter cell is drawn through the circular central opening so 

 formed in the septum into the adjoining cell-cavity. 



At times the lignified portion of the septum is so delicate 

 that, after the operation of a solution of glycerine, only a very 

 slender annular thread is visible on the inner surface of the 

 mother cell ; and it might be supposed that the two adherent 

 contracted secondary daughter cells floated freely in the centre 

 of the mother cell. Upon the addition of a diluted watery solu- 

 tion of iodine, which is greedily taken up by the fluid contents 

 of the primary cell, it is perceived, by the movements thereby 

 induced within the two contracted and coherent daughter cells, 

 that these do not float freely in the centre, but are fixed in their 

 position by the thread-like annular septum, which, from the 

 cloudiness of the cell-fluid, caused by the solution of iodine, 

 appears like an extremely thin clear lamina, and exhibits slight 

 movements cori'esponding with those of the daughter cells. 



