8'2 PLANTS OP NEW ZEALAND 



and the Oil Palm together furnish sugar, starch, oil, resin, cordage, writing 

 materials, material for building and thatching, edible fruits, pleasant beverages, 

 vinegar, soap, etc. The palms reach their southernmost limit in New Zealand. 



The stem of the pahii differs greatly in structure from 

 that of other trees. The ordinary forest tree grows in 

 thickness by depositing fresh layers of tissue between the 

 wood and the bark. If a felled trunk be observed, it will 

 be seen at once that there is or has been a central pith, and 

 around this, concentric shells of wood have been deposited. 

 In young [)lants, the pith occupies a considerable portion of 

 the stem, in old trees it becomes obsolete. The stem of the 

 mature tree is, in fact, made up of a series of hollow cylinders 

 of woody tissue tapering to the top, and placed one inside the 

 other. The growth of such a stem is due to the presence of a 

 generating tissue immediately below the bark, which annually 

 gives rise to a layer of wood. Each woody sheath is in 

 reality made up of a number of longitudinal strands or bundles 

 (the fibro- vascular bundles). Between the bundles, lines may 

 be seen radiating out from the centre to the outer edge of the 

 wood. These are the medullary or pith rays. The bundles 

 comprising such a trunk are said to be open, because the 

 generative tissue does not become exhausted, but the stem 

 continues to grow in thickness from year to year. Such a 

 structure is typical of the stem of a pine or dicotyledon. 



On the other hand, in a monocotyledonous tree, such as a 

 palm, the pith always constitutes a considerable portion of the 

 stem, and the woody bundles are scattered through it, not 

 arranged in a circle round it as in the dicotyledons. Such 

 bundles are no longer capable of growth in thickness, as the 

 generating tissue is exhausted in their production. They are 

 therefore said to be closed. The stem of a palm-tree therefore 

 tapers but little, and cannot go on increasing in thickness. 

 This is typical of a monocotyledon'". 



* The stem of the calibage-tvee, Cnnhjliiie, is exceptional. 



