STRUCTURE OF STEMS 55 



from the cambium or meristem. At first they elongate, and the 

 cross walls at their adjacent ends dissolve and thus make long 

 tubes or vessels of the connecting cells. These different kinds of 



Fig. 54- 

 Uncoiled spiral ducts of Indian lotus. 



vessels can often be found in the same bundle. In some plants 

 the spiral thickenings on the vessels are so regular and so strong 

 in contrast with the thinner portions of the wall and the other 



Fig. 55- 

 Photomicrograph of uncoiled spiral ducts of Indian lotus. 



tissues that when the stem is broken the spiral will uncoil in long, 

 delicate, cobweb threads. This is shown in a remarkable way in 

 the flower stems and petioles of the Indian lotus (figs. 53-55). The 

 rind of the stem is cut with a knife and the stem then broken. 



