54 



PRACTICAL BOTANY 



asparagus or corn stem (Fig. 38). No such complicated bark 

 as that of woody dicotyledons is found in monocotyledons. 



51. Growth in thickness of the monocotyledonous stem. The 

 very young stem of monocotyledons may for a time increase 

 considerably in diameter by the formation within it of new 

 bundles. But in monocotyledons all the cambium becomes 



FIG. 38. Cross section of a corn stem (monocotyledonous) 



c, cortex ; &', small fibro vascular bundles near the cortex ; 6, large bundles in the 

 interior of the stem ; p, pith-like material between bundles. About one and one- 

 half times natural size 



changed into other tissues, so that none is left (as it is in 

 dicotyledons) to develop new tissue. In monocotyledons the 

 bundles are said to be closed, while those of dicotyledons in 

 which active cambium remains are said to be open. Most 

 monocotyledonous trees, such as the palms, cannot form an- 

 nual rings of wood. A few tree-like monocotyledons have 

 trunks which continue for many years to increase in thickness, 

 but the thickening of the trunk takes place in a manner wholly 



