56 PKACTICAL BOTANY. 



Put on a high power, and observe the form of the initial cell? 

 and its relation to the adjoining tissues : it will then be noted 

 that segments are cut off alternately from either side, and then 

 one from the base. The lateral segments undergo further 

 divisions according to the type of the limiting layer ; the basal 

 segments divide up, and ultimately pass over into medullary 

 tissue. 



If sections through the apex be stained with hsematoxylin, it 

 may be observed that each cell contains a single nucleus : this 

 observation may also be extended to the tissues of the older parts 

 of the thallus. 



VII. Cut successive transverse sections of the apex, 

 so as to pass immediately below the base of the de- 

 pression : one of these sections will include the initial 

 group, which will then appear to be composed of some 

 four or five cells, of oblong form, placed in a row, 

 side by side. 



Examining these under a high power it may be seen that seg- 

 ments are cut off (l)from either side of their oblong outline, (2) from 

 the sides of those of the initial cells which are at either end of the 

 row, and (3) that any of the initial cells may divide by a median 

 wall into two similar cells : by the latter process the number of 

 initial cells may be increased, and this is usually the case before 

 dichotomy, which is brought about by the cells at the middle of 

 the row ceasing to act as initial cells, and passing over into the 

 condition of permanent tissue, while those at either end of the 

 row retain the character of initial cells, and are to be recognised as 

 the two independent initial groups of the new branches : thus the 

 branching is a dichotomy. The attempt should be made to find 

 sections illustrating this process of branching. 



This type of apex is by no means constant for the Fucoids j. 

 thus in Himanihalia there has been found in each branch of the 

 thallus only a single apical cell, which appears triangular in 

 transverse section, but in longitudinal section it shows two con- 

 vex sides : the form of the cell is thus, roughly speaking, that of 

 a Brazil nut. 



