viii THE HISTOLOGY OF THE TISSUES 101 



the stem until it joins on to the bundle below. The above are 

 the arrangements in most dicotyledonous plants. 



The course of the bundles in monocotyledonous plants is very 

 irregular. The bundles from any leaf base pass into the stem 

 towards the centre, then bend back and pass for some distance 

 down the stem, when they join on to the bundles below. 



EXPT. 93. Obtain a piece of the stem of the Wallflower with a 

 number of leaves on it, and trace out the course of the vascular bundles. 

 To do this bisect it longitudinally so as to pass through the middle of a 

 leaf ; clear away the pith with a blunt knife. Note 



(i) That the bundle which enters the stem from the midrib of the leaf 

 runs inwards for a short distance, then turns straight downwards, and 

 ioins on to the leaf vertically below the first leaf. 



(ii) That the bundle runs through five internodes without joining a 

 bundle. 



(iii) That there are two smaller bundles that act in the same way. 



(iv) That in any section of the stem of the Wallflower there must be 

 five large bundles and ten small bundles cut through. 



EXPT. 94. Trace the course of the vascular bundles in the stem of 

 the Deadnettle. Bisect the stem longitudinally, so as to pass through 

 two leaves on the same side of the stem. Clear the pith away, and 

 note 



(i) That the bundle which enters the stem runs inwards and then 

 downwards, and joins on to the bundle of the leaf vertically below. 



(ii) That the bundle only passes through two internodes before it 

 joins on to the bundle below. 



(iii) That in the stem of the Deadnettle there are four main vascular 

 bundles, which correspond to the decussate arrangement of the leaves. 



THE GROUND TISSUE. 



The Ground Tissue. The tissue which is found in the 

 centre of a stem and between the vascular bundles and the 

 epidermis is called ground or fundamental tissue. It 

 usually forms the principal part of the primary tissue of the 

 plant, and can be arranged in three groups : 



The Pith within the ring of vascular tissue. 



The Cortex between the ring of bundles and the epidermis. 



The Medullary rays between the pairs of bundles. 



The vascular bundles seem to be fixed in the ground tissue, 

 which in a young stem appears to surround them. It may 

 contain chlorophyll and be used for obtaining food. 



While the epidermal tissue protects the internal parts of the 

 plant and the vascular bundles perform the office of conduction 

 and support, the ground tissue provides for the nutrition of the 

 plant and forms a store for reserve material. 



