CHAPTER IX 



THE HISTOLOGY OF THE SHOOT AND ROOT 



The Structure of a Dicotyledonous Stem. A trans- 

 verse section of a young dicotyledonous stem, when examined 

 under the low power of the 

 microscope, shows the follow- 

 ing parts (Fig. 128). Exter- 

 nally the section is limited by 

 a single layer of cells, many 

 of which may produce hairs ; 

 this is the epidermis. Inside 

 the epidermis comes the cor- 

 tex, bounded on the inside by 

 a single row of cells called 

 the endodefmis. Inside 

 the endodermis a broken ring 

 of vascular bundles is found, 

 which is surrounded on the 

 outside by a layer of cells, 



known as the pericycle/ The vascular bundles are divided from 

 one another by a number of cells forming medullary rays. 

 The centre of the stem is full of loose cells which form the pith. 



FIG. 128. Transverse section of young 

 stem of Sunflower, showing ten sepa- 

 rate vascular bundles in the ground 

 tissues. Ef>, epidermis ; co, cortex ; 

 Pi, pith ; Pit, phloem ; cb, cambium ; 

 xy, xylem. 



Outside. 

 Epidermis . 

 Cortex . . \ 

 Endodermis j 

 Pericycle . \ 

 Phloem . . \ 

 Cambium . I 

 Xylem . . I 

 Pith .... 



Inside. 



Epidermal Tissue 

 Ground Tissue . 



Vascular Tissue 

 Ground Tissue 



Transverse 

 Section of 

 Dicotyledonous 

 Stem. 



