THE HIGHER CRYPTOGAMIA. 269 



ing the axis of the stem, it occurs at least once in the cells 

 of the circumference. On the upper surface of the stem 

 therefore an extremely regular circular girdle of cells is to 

 be distinguished. At a definite distance from the apex of 

 the terminal bud all its outer cells which lie at the same 

 altitude (a girdle of cells enclosing the end of the stem) 

 divide contemporaneously by a septum inclined to the 

 horizon (PL XXXV, fig. 2). In the outer (the upper) of 

 the two cells thus formed, a division takes place by a sep- 

 tum inclined in an opposite direction. Thus an annular 

 wall of uniform height and embracing the terminal bud is 

 raised a little beneath the apex of the latter : this is the 

 first rudiment of the youngest leaf. All the cells of its free 

 upper edge continue to divide by alternately inclined septa 

 (PI. XXXV, fig. 1). The leaf at first grows upwards in 

 the form of a cylindrical sheath of uniform height enclosing 

 the terminal bud (PL XXXV, figs. 6, 7). 



The place of origin of the youngest leaf, the girdle of its 

 mother-cells, is close above the place of attachment of the 

 next younger leaf. The leaf very soon after its production 

 begins to increase in thickness, the cells of its base, — those 

 of the under surface exclusively (PL XXXV, fig. 1), — 

 dividing repeatedly by septa parallel to this surface. This 

 cell-multiplication progresses slowly from the base of the 

 leaf to its apex, and finally ceases at a considerable distance 

 beneath the latter. The outer (or lower) ones of the cells 

 thus formed, divide by transverse septa (septa parallel to 

 the ideal longitudinal axis of the leaf) the division being- 

 more frequent in proportion as the shoot is destined fur 

 more vigorous development. The great excess in the 

 number of the cells of the under surface of the leaf over 

 that of the upper, causes the free upper edge of the leaf 

 to bend inwards. By the vigorous multiplication of the 

 lower portion of the outer surface of the leaf, the base of 

 the leaf is soon transformed into numerous layers of cells, 

 parallel to the longitudinal axis of the shoot, and repre- 

 senting the outer circumference of the stem (PL XXXVI, 

 fig. 1). The subsequent increase in length and thickness 

 of the joints of the stem depends upon the increase in 



