170 



THE GROWTH OF ROOTS AND STEMS. 



* (6) Cut transverse sections of a Bean root at different levels, starting 

 a little behind the root-tip ; it is easier to do this if the root is held 

 between two grooved pieces of elder-pith or of carrot. Keep your razor 

 wetted with 50 per cent, spirit, cut thin sections, stain some with 

 aniline chloride, others with iodine solution. 



Notice the tissues shown in Fig. 58, the skin-layer, many of whose 

 cells grow out to form root-hairs ; the rind (cortex) consisting of cells 



- ENDODERMIS 



PERICYCLE 



-PROTOXYLEM 



Fig. 58. Transverse Section of a Young Root of a Dicotyledon with Pour 

 Strands of Wood. 



which are separated at the corners by air-spaces and often containing 

 starch-grains ; the central cylinder consisting chiefly of the wood- 

 bundles (stained yellow with aniline chloride), the bast-bundles 

 (phloem) alternating with these, the packing-tissue between the 

 bundles, and the sheath surrounding the whole cylinder. The inner 

 wood- vessels are pitted, the outer ones are spiral ; the latter are narrow 

 and are formed before the inner vessels, hence the term " protoxylem " 

 is applied to these outermost and narrowest vessels. The bast-bundles 



