THE BIOLOGY OF A PLANT. 



and left sides. These cells in turn continue to grow and divide 

 and thus give rise to two similar masses of rueristem, which 

 together constitute the apical bud. From the meristem by grad- 

 ual, though rapid, changes the various tissues of the adult rhi- 

 zome are differentiated ; and longitudinal sections passing through 



a.c. 



FIG. 42. (After Hofmeister.) Apical cell of the 

 rhizome in a vertical longitudinal section, a.c, 

 apical cell; h, hair; m, meristem. 



FIG. 43. (After Hofmeister.) Apical 

 cell of the rhizome in horizontal lon- 

 gitudinal section, u.c, apical cell. 



the lateral ridges show the mature tissues fading out in a region 

 of indifferent meristem about the apical cell (Fig. -A3). 



The apical cell lies at the bottom of a funnel-shaped depression at the 

 tip of the stem. It is shaped approximately like a thin, two-edged wedge 

 with an arched or curved base turned forwards towards the centre of the 

 funnel-shaped depression. The thin edge of the wedge is directed back- 

 wards, and its sides, which are also curved, meet in a vertical plane 

 above and below. A longitudinal section taken through the plane of the 



a>c 



FIG. 44. (After Sachs.) A vertical transverse section through the apical cell, a.c, showing 

 a boundary of hairs and a second apical cell, I, belonging to a leaf. 



lateral ridges therefore shows the apical cell in a triangular form as in Fig. 

 43. A section taken at right angles to this ?'.e., vertical and longitudinal, 

 shows the cell to be approximately rectangular and quadrilateral (Fig. 

 42), while a transverse vertical section shows it in the form of a bi-couvex 

 lens (Fig. 44). 



