4 HOFMEISTJ5R, ON 



angles to the free outer surface of the stem (PI. I, figs. 3, 

 4). The outer one of the cells thus formed continues to 

 divide by septa parallel to the free outer surface, until the 

 cells have reached the number of Avhich the shoot is des- 

 tined to consist in the direction of its thickness. This 

 number (about thirteen) is greatest in the median line 

 of the shoot, and diminishes to one at the sides. The 

 arrangement of the cells of a section of the end of a 

 growing shoot, taken through the median line at right 

 angles to the surface, is what is called scalariforni; 

 the cells of each longitudinal moiety of the shoot are ar- 

 ranged in rows parallel to one another bearing upwards 

 from the lonoitudinal axis. Each of the cell-masses which 

 unite to form a shoot consists in its earliest stage of a single 

 cell, situated normally at the bottom of the indentation of 

 the fore edge of an older shoot (PI. I, fig. 7), but, when des- 

 tined to form an adventitious shoot, placed at the edge or on 

 the surface of such older shoot. The primary division of 

 this cell, which takes place by a septum inclined to the 

 horizon, is followed immediately by the division of the 

 cells of the first and second degree, by means of a longitu- 

 dinal septum perpendicular to the surface of the stem. As 

 the young shoot increases in length, the number of its cells, 

 reckoned in the direction of its breadth, increases largely 

 and continually, the cells of its fore edge dividing in like 

 manner by longitudinal septa. Thus it happens that, as 

 long as the shoot grows, its fore edge becomes continually 

 wider. The arrangement of the cells seen from the sur- 

 face is flabelliform, in rows which radiate from the base of 

 the shoot to the arcuate fore edge. In each of the cells 

 which constitute the permanent upper and under surface of 

 the shoot, four cells are produced by duplicate cell-divi- 

 sions, which four cells lie in one plane. It follows that, in 

 full-grown shoots, these superficial shells are four times 

 smaller than the internal cells. A suppression of the final 

 septum not unfrequcntly occurs in individual cells of the 

 inner parenchyma. Some of the latter are often found 

 which are twice the size of the adjoining cells. 



The growing cells of the fore edge of young shoots con- 

 tain a thick coating of a mucilaginous fluid rendered tur- 



