Lecture XXV. 



217 



conspicuous intercellular spaces, which are more striking in the 

 neighbourhood of the stomata. The cells of the deeper layers of 

 the cortex are poorer in chloroplasts, and close to the connecting 

 tracts its cells possess few or none ; but they often contain numbers 

 of starch granules. The cells of the medullary rays and pith are 

 similar to those of the inner cortex, and sometimes contain even 

 larger amounts of starch. The cells of the pith extend for only a 

 few layers inside the conducting tracts, the whole axial region of 

 the stem being occupied by the central cavity. 



FIG. 74. Ranunculus repens> stem, transverse section, x 10. a, epidermis; 

 b, cortex ; c , medullary ray ; rf, pith ; e, space in pith ; /, bundle-sheath ; 

 g, bast; h, wood. 



The conducting tracts or vascular bundles form very distinct 

 cords of tissue traversing the fundamental tissue in a longitudinal 

 direction. They are formed like those in the young Pine stem of 

 two parallel strands the wood (xylem) and the bast (phloem). 

 These tracts stand out more from the surrounding tissues than do 

 those of the young Pine stem. This is chiefly due to the fact that 

 each tract is enclosed in a tubular sheath of tough and fibrous 

 tissue the bundle-sheath. But the most important difference 



