2o8 MONOSTROMA, ULVA, AND NITELLA less, xx 



common in vegetable cells in which, owing to the confining 

 cell-wall, no freer movement is possible. 



The numerous nuclei (e, nu) are rod-like and often 

 curved : they can be seen to advantage only after staining 

 (Fig. 45). Lying as they do in the inner layer of protoplasm, 

 they are carried round in the rotating stream. 



In the general description of the plant it was mentioned 

 that the stem ended distally in a terminal bud (Fig. 44, a, 

 term, bud) formed of a whorl of leaves with their apices 

 curved towards one another. If these leaves (f, Z^) are dis- 

 sected away, the node from which they spring {iid'^) is found 

 to give rise distally to a very short internode {int. nd"^), 

 above which is a node {nd^) giving rise to a whorl of very 

 small leaves (/''), also curved inwards so as to form a bud. 

 Within these is found another segment consisting of a still 

 smaller internode {int. nd^) and node, bearing a whorl of 

 extremely small leaves {P), and within these again a segment 

 so small that its parts {int. nd*, I*) are visible only under 

 the microscope. The minute blunt projections (/■*), which 

 are the leaves of this whorl, surround a blunt, hemispherical 

 projection {gr.pt), the actual distal extremity of the plant — 

 the growing point or piinctujn vegetationis. 



The structure of the growing point and the mode of 

 growth of the whole plant is readily made out by examining 

 vertical sections of the terminal bud in numerous specimens 



(Fig. 45)- 



The growing point is formed of a single cell, the apical 

 cell (a, ap. (t), approximately hemispherical in form and about 

 ■i^ mm. in diameter. Its cell-wall is thick, and its cell-body 

 formed of dense granular protoplasm containing a large 

 rounded nucleus {nu) but no vacuole. 



In the living plant the apical cell is continually undergoing 

 binary fission. It divides along a horizontal plane, i.e., a 



