Origin ok tiik wood. 117 



feed in iu» iinj)ortant rcsprcl. Tliey sciul \:\) tlic asceiuling 

 axis in llie form of a biaiicii, nnd tlu' dtscnidini; axis in llie 

 form of vascular tiUrts, wfiicli imiti'd, lorni llic :?UMn and tcr- 

 minale in liie earih, moJilicd in sonic respect, by ihc cellular 

 sysleii), f«»rmin«^ what, taken a^ a whole, is called the wood. 

 The various V'»rieties of wood are produced l»y llie action of 

 tlic cellular system. Of this we may he convinced hy rc- 

 movint{ a nni:; of hark of one tree and supplying the place 

 of the rem»>ved portion by u rinj^ from a dilVerenl tree, and 

 liie wood fornied under the strange jiorlion wdl be of the 

 iame kiml as the tree Ooni which it was taken, but the wood 

 above ami below will remain unaltered. The same is the 

 case with «.n-a(ts. The jrrafl will always remain unaltered, 

 while tlie wood of the stock remains unatVected by tiie graft. 



14(3. 'J'he truth of the assertion that the wood is composed of 

 roots of leaves is abundantly shown by all endogenous trees. 

 Each bundle of woody libre in the Yucca or Pahnello, may 

 be traced directly to the base of a leaf, and if a root is the 

 descending a.\is, each bundle must be considered a root pro- 

 ceeding from a leaf, and the stems as composed of innumer- 

 able roiits found toi-ether by the cellular tissue. I\o theory 

 that has ever been proposed lias explained, with any degree 

 of gntisfacMon, the growth of Endogens, but this theory of 

 DuPctit Thoiiars explains, with perfect simplicity, every va- 

 riety of vefjetable production. 



in exoffeiis we find abund mt evidence < fits truth. If the 

 leaves be removed from the extremity of a branch, no in- 

 crease of the branch will take place, exct pt below a leaf, 

 and the branch will die, down to the first leaf, and on the op- 

 posite side it will die lower down if the leaves are alternate. 

 Tliis fact shows, beyond doubt, that the production of >vrM)d 

 depends on depositions from the leaves. 



147. The case of Endorjens before adduced, shows ns clearl v 

 that the woody fibres are produced from the leaves down- 

 wards. Some uncommon examj)les are upon record, which 

 gt) still firiher to cindirm the pcsition. In tlu! Pandanus 

 the stem near the ground is extremely slender ; higher up 

 it is thicker and gives out aerial roots, which act as props to 

 the plant by enterini; the earth oblupn-ly. The aerial rof>t3 

 are beyond doubt what would have composed a jtart of the 

 stem, bad they rf^mained bound by the c« llular substance 

 into one o^linder, but from some ( nnse thev separate nnd 

 subtract so ni'ich from the mai«s of the stem near the root. 

 Prof. Lindlcy describes another instructive case on this sub- 

 ject ill the Burbacenia from Rio Janeiro, recently discovered 



