STRUCTURE OF STEMS 6 1 



trees. For this reason the trunks of palms are of nearly equal 

 diameter while dicotyledonous trees and conifers which have 

 open bundles (paragraphs 104, 105) have tapering trunks. 



Uncoiled spiral ducts of Indian lotus. 



101. In a longitudinal section the vessels of the bundle are 

 seen to be marked in various ways by thickenings on the wall. 

 These markings are in the form of rings, spirals, pits, transverse 



Fig. 58. 

 Photomicrograph of uncoiled spiralducts of Indian lotus. 



thickenings. These vessels were derived from cells of the 

 fundamental tissue.* At first they elongate, and the cross walls 



* Parenchyma, which of course originally came from the cambium or 

 meristem (paragraph 61). 



