THE HIGHER CRYPTOGAMIA. 141 



ably in width. Reckoning from the youngest leaf backwards, 

 the sixth leaf of a shoot embraces one half of the stem ; the 

 twelfth embraces from five eighths to six eighths. Inasmuch 

 as, during the multiplication of the cells of the base of the 

 leaf, the cells of the stem upon which they are seated are 

 in an active state of multiplication in a tangential direction, 

 it follows that the place of attachment of the leaf to the 

 stem continues, relatively, of a considerable width, amount- 

 ing to one third of the circumference of the stem. Every 

 section made through that part of a principal shoot which 

 lies nearly under the apex meets, not only the longitudinal 

 line of each eighth leaf, but also lateral portions of five 

 intermediate leaves ; so that, in most cases, the points of 

 insertion of two leaves are only separated by one cell of the 

 cortical layer. 



When the division of the apical cell of the leaf (which 

 division takes place by means of septa diverging alternately 

 from the median line) ceases, a multiplication of all its cells, 

 excepting those of the margin, commences ; this multipli- 

 cation begins at the tip, and progresses rapidly from thence 

 to the base. Each of the square cells divides into two 

 rather unequal parts by means of a septum parallel to one 

 of the sides, but not exactly traversing the middle point of 

 the cell (PI. XVIII, fig. 2, below, to the left). The larger 

 of the two is then divided, by means of a septum parallel 

 to the narrow sides, into tw r o cells of unequal size, the 

 larger being square and the other somewhat elongated 

 (PI. XVIII, fig. 2). After the termination of these divi- 

 sions the surface of the leaf consists of a system of 

 square cells, each of which is surrounded by four oblong 

 cells. 



In the oblong cells chlorophyll-granules are produced, 

 which increase rapidly and considerably in number and in 

 size (PI. XVIII, figs. 3, 9). On the other hand, the pale- 

 green, highly refractive, and finely granular mucilage, which 



elusion which I had previously drawn from similar appearances ('Abhandl. Kon. 

 Sachs. Ges. d. Wissensch.,' vol. iv, p. 161), viz., that the growing power which 

 regulates the form of compound vegetable organs is mainly proportionate to 

 the form and number of the new cells in process of production, and that such 

 power does not exhibit itself in each peculiarity of the process of cell-multipli- 

 cation. 



