244 



Practical Plant Biology. 



in the Dicotyledons or in the Gymnosperms. The difference is 

 most easily appreciated in a transverse section. As we have seen, 

 the conducting strands of a Dicotyledon form a circle in a transverse 

 section of the stem. In a Monocotyledon, on the other hand, they 

 appear irregularly scattered. Some are to be seen in the central 

 region of the section. They have entered from leaves attached 

 just above the level of the section. Those near the cortex are 



f. 



HHD 



FIG. 88. Scilla nutans, flower-stalk, transverse section, x 45. a, cuticle; 

 b, epidermis ; c, fundamental tissue ; d, conducting tract or vascular 

 bundle ; e, wood or xylem ; /, bast or phloem. 



those which have come from leaves inserted at a higher level. 

 The conducting tracts are largest just after they enter the stem and 

 they taper gradually downwards. Hence the conducting tracts in 

 the central region of transverse section are larger than those nearer 

 the periphery. In structure the conducting tracts of the Mono- 

 cotyledons resemble generally those of the Dicotyledons, but they 

 never possess a cambium layer between the wood and the bast 



