168 



PRACTICAL BOTANY 



The structure and mode of origin of the young leaves should 

 also be observed in the median longitudinal sections. 



The Root. 



XII. Cut transverse sections of the root of the Male Fern, 

 selecting for that purpose the thickest part of an old root : 

 mount in glycerine, and observe 



i. The piliferous layer : certain cells of this superficial layer 



FIG. 12. Diagram showing the arrangement of cell-walls as seen in a median longi- 

 tudinal section through an apical cone with a pyramidal apical cell. A A, are 

 the segmental walls, which form part of the system of anticlinals ; a, a, walls by 

 which each segment is cut into two equal halves : these complete the anticlinal 

 curves ; P P, periclinals, which are not completed up to the apex. (After Sachs.) 



have grown out as root-hairs, remnants of which may still be 

 seen. 



2. The greater part of the section consists of the bulky, 

 brown-walled cortex, of which the outer parts are thin-walled ; 

 but, passing inwards, there is a sudden increase in thickness 

 of the wall, so as to form a dense sclerenchymatous ring ; this 

 surrounds 



3' The endoderms, which consists of a single layer of cells 



