270 HOFMEISTEB, ON 



length and breadth of this cellular mass which has arisen 

 from the development of the basal portion of the leaf-rudi- 

 ment. The central cellular cylinder of the stem which has 

 arisen immediately from the terminal bud becomes exclu- 

 sively pith.* In the mean time by longitudinal division of 

 the cells of the leaf in a direction radial to the axis of the 

 stem — a division which occurs as well in the cells of the 

 under part which represents the outer layer of the stem, as 

 also in the free sheath-shaped upper portion — the number 

 of the cells of the circumference of the stem-joint and of the 

 hollow cylindrical leaf continually increases. 



Shortly after the first appearance of the leaf there may 

 be observed an inequality in the activity of the growth of 

 its free upper edge. In the first place, at four points of 

 the leaf, one of the cells is about one step in advance of 

 all the rest in the process of division, which division takes 

 place by septa turned alternately towards and away from 

 the longitudinal axis of the stem (PL XXXV, fig. 8). The 

 neighbouring cells on the right and left are about one step 

 in arrear -. the cells adjoining the latter cells remain one 

 step further in arrear. Four short blunt points are thus 

 produced, placed in pairs opposite to one another upon the 

 upper edge of the sheath-like leaf. The multiplication of 

 the cells of the circumference of the free upper edge of the 

 leaf is produced exclusively by the division of the apical 

 cells of these points by means of longitudinal septa 

 (PI. XXXV, fig. 8).f This division of the apical cells of 

 the tip of the leaf by septa radial to the circumference of 

 the leaf-sheath is often repeated at certain stages of the 

 growth of the leaf, and increases the breadth of the tip 

 more and more. Shortly afterwards the widened apex of 

 the tip of the leaf exhibits the first indication of a rapid 

 bifurcation (PL XXXV, fig. 9). Thus with the age of the 

 leaf the number of the teeth of its edge increases; in 



* From an opposite point of view, viz., the comparison of finished stages of 

 development, Spring arrives at the same conclusion for larger divisions of the 

 vegetable kingdom ('Monographie des Lycopodiacees, estraite des Memoires de 

 l'Academie Royale de Belgique,' Bruxelles, 1849). 



f This mode of growth of the tip of the leaf brings strongly to mind that of 

 the shoots of Riccia, &c. 



