and Development of Marsilea. 421 



superficial cells, and then continues dividing, sometimes by 

 transverse and sometimes by longitudinal walls. The inner cell, 

 which is now the true apical root-cell, proceeds to separate lateral 

 cells of division alternately in three directions, which likewise 

 originate the very uniform tissue of the root by longitudinal 

 and transverse septa. At first, however, this process takes place 

 very slowly. 



The most rapid progress is made by the first leaf. Its primi- 

 tive cell is first broken up, simultaneously with the two sub- 

 jacent cells of the anterior half of the germ, into two equal 

 lateral halves, in a plane standing perpendicular to the first 

 three divisional walls. In both, the further division takes place 

 by the production of divisional walls alternately from above and 

 from the front, tending towards each other internally, separating 

 discoid cells from the apical cell, which is rising forwards and 

 upwards. In this way the leaf soon acquires a conical form, 

 constantly becoming more acute, which finally passes, by the 

 repeated extension and division of the cells of the second and 

 third order, into the filamentous form, which the first leaf 

 retains. 



The evolution of the bud takes place but slowly. Its primi- 

 tive cell is divided by the above-mentioned perpendicular septum 

 into two adjacent cells, which are apparently similar, but are of 

 very unequal value. One of them becomes the second leaf: the 

 other continues to be the apical cell of the incipient axis of the 

 stem ; and thus the symmetry of the anterior side of the germ 

 is for the moment destroyed. 



In the apical cell, three septa approximating internally, and 

 running nearly parallel to the three lateral walls, separate three 

 more divisional cells — first an upper [one, then a lower one, 

 and lastly an inner lateral one adjacent to the second leaf: they 

 leave the apical cell diminished between them, and arc developed 

 from no independent parts. The axis of the apical cell, which 

 is now of a three-sided pyramidal form, furnished with a strongly 

 arched basal surface directed forward, now exactly indicates the 

 direction of the further development of the stem-bud. A seventh 

 septum, running similarly to the fourth, but more strongly 

 cui-ved downwards on the side opposite to the second leaf, and 

 cutting off a larger daughter cell, gives origin to the third leaf, 

 which consequently makes its appearance opposite to the second, 

 and restores the symmetry of the bud. 



Next trimerous cycles of interstitial cells issue from the apical 

 cell, corresponding to its three walls, until the fourth and fifth 

 leaves are produced from it in the same direction and in the 

 same manner as the second and third. No law could be dis- 

 covered for the number of these interstitial cells, which rapidly 



