80 



PRACTICAL BOTANY 



their order of development is thus acropetal. The 

 surfaces of the older leaves are covered with 



3. Hairs, which are absent from the apical cone 

 and the youngest leaves, the hairs being developed 

 subsequently to the leaves themselves. 



Note (with a higher power) that the apical cone itself 

 consists of thin-walled cells with plentiful protoplasm, 

 which are smaller than the cells of the mature tissues 



V j 



FJG. 5. Diagram illustrating the plan of arrangement ot cell-walls in the apex ot 

 the stem of an Angiosperm. x, x = longitudinal axis, which is the organic 

 axis of the stem. E, E = external surface. P,P, P,P, are the periclinal curves. 

 A, A = the anticlinal curves which cut these at ri^ht angles. p,p= incom- 

 plete periclinals. a, a = incomplete anticlinals. The dermatogen is repre- 

 sented by the space between the outer surface, E, E, and the outermost 

 periclinal, p, p. (After Sachs.) 



already studied, and are in a state of active division, 

 i.e. they are merismatic. Observe further that the 

 newly -formed cell-walls cut the pre-existing cell-walls 

 at right angles, and that the two parts of the cells thus 

 divided are apparently equal to one another. A com- 

 parison of the general arrangement of the cell-walls 

 with the diagram shown in Fig. 5 will help to make 



