20 



SOUTH INDIAN GRASSES 



numerous small thick-walled cells lying between the pitted vessels 

 constitute the xylem. Just above the xylem there is a group of 

 large and small thin-walled cells. This is the phloem and it 



k*\ i h 



FlG. 23. —Longitudinal section of a vascular bundle. x 250 



1. Annular vessel : 2. spiral vessel; 3. pitted vessel : 4. sieve tubes or phloem ; 



5. sclerenchyma. 



consists of sieve tubes and thin-walled cells. All round the xylem 

 and the phloem there are many thick-walled cells. These are 

 really fibres forming the bundlc-shcath. On account of this 

 bundle-sheath the bundles are called fibro-vascular bundles. 



Structure of the stem. —The stem of a grass consists of a mass 

 of parenchymatous cells with a number of fibro-vascular bundles 



-^iV',;'^.' 



PlG. 24. — Transverse section of a portion of the stem of Rottboellia exaltata- * 70 

 r. Epidermis ; 2. sclerenchyma ; 3. vascular bundle. 



