88 GENERAL BOTANY 



the plant is a month old, the vessels and tracheids 

 are separated from the sieve-tubes and companion- 

 cells (phloem) by the cambium, which forming as we 

 have learnt, fresh wood (vessels, tracheids, fibres and 

 some parenchyma), on its inside, and fresh phloem 

 (sieve-tubes and companion-cells), with some fibre 

 and parenchyma, on its outer, makes the hard central 

 cylinder of wood, and the outer covering of bark. Thus 

 we see that there is a fundamental difference in structure 

 between the stem or root of a monocotyledon and that 

 of a dicotyledon. The former is composed mainly of 

 vascular bundles which have run down from the leaves, 

 those from the higher ones joining others lower down, 

 the latter of a secondary tissue, the cambium-formed 

 woody cylinder and bark, to which the leaf bundles are 

 attached, the wood to the wood, the phloem to the 

 phloem. 



