54 



GROWTH AND WORK OF PLANTS 



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

 cells with thick whitish walls, the bast portion of the bundle. The 



dividing cells of the cambium fur- 

 nish the cells to make these different 

 elements of the bundle which soon 

 cease to grow and form permanent 

 tissue. The cambium then disap- 

 pears; vessels, bast, and thick-walled 

 fibers remain. This thick-walled 

 fibrous tissue in the monocotyledons 

 entirely surrounds or encloses the 

 growing tissue and other elements 

 of the bundle and 

 soon prevents far- 

 Fig. 52. ther enlargement 



Transection of fibro-vascular bundle of j 



Indian corn, a, toward periphery of and expansion. 

 stem; g, large pitted vessels; s, spiral ves- c i i ji 



sel; r, annular ve<*el; /, air cavity formed ^UCh a bundle in 

 by breaking apart of the cells; i, soft bast, i i, 4-U ,~U' 



a form of sieve tissue; p, thin-walled paren- which the Cambium 



is enclosed by and 



passes over into permanent tissue is called a 

 closed 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 trees, because 

 the trunks cease to increase in diameter. For 

 this reason the trunks of palms are of nearly 

 equal diameter while dicotyledonous trees and 

 conifers which have open bundles (paragraph 98) 

 have tapering trunks. 



95. In a longitudinal section the vessels of 

 the bundle are seen to be marked in various 

 ways by thickenings on the wall. These mark- 

 ings are in the form of rings, spirals, pits, trans- p^ 016 - 

 verse thickenings. These vessels were derived from cells of the 

 fundamental tissue (parenchyma) which of course originally came 



pig. 53. 



O l f lp se ^ ion in f 



