6o 



GROWTH AND WORK OF PLANTS 



are seen the large vessels with the smaller fibers and some 

 thin-walled parenchyma cells. This is the woody portion of the 

 bundle. Upon the other side of the bundle is a group of small 

 cells with thick whitish walls, the bast por- 

 tion of the bundle. The dividing cells of 

 the cambium furnish the cells to make 

 these different elements of the bundle 

 which soon cease to grow and form perma- 

 nent tissue. The cambium then disap- 

 pears; vessels, bast, and thick-walled 



Fig. 55- 



Transaction of fibro-vascular bundle 

 of Indian corn, a, toward periphery of 

 stem; g , large pitted vessels; s, spiral 

 vessel; r, annular vessel; /, air cavity 

 formed by breaking apart of the cells; 

 i, soft bast, a form of sieve tissue; p, 

 thin-walled parenchyma. (Sachs.) 



Fig. 56. 



Uncoiled spiral 

 ducts, from petioles of 

 Indian lotus, support- 

 ing weight of section 

 of petiole. 



fibers remain. This thick-walled fibrous tissue in the mono- 

 cotyledons entirely surrounds or encloses the growing tissue 

 and other elements of the bundle and soon prevents farther 

 enlargement and expansion. Such a bundle in which the 

 cambium is enclosed by and passes over into permanent 

 tissue is called a dosed bundle. Stems with closed bundles 

 usually do not increase in thickness after the formation of the 

 permanent tissue. Monocotyledonous trees like the palms, 

 therefore, never attain the great diameter of dicotyledonous 



