Woody Fibre of the Stems of Palms. 61 



habit of seeing old palms cut down knows this to be the fact. 

 When the axe is laid to the bottom of some of these old stems, 

 it rebounds from them as if it were striking a piece of iron, 

 while the upper part can be cut through with the greatest 

 facility. Every Brazilian is aware of this fact. So durable 

 is the wood of the large species of palm which they call Pati, 

 that they prefer it to most other wood for supports to their 

 houses, which in the country are generally built of wood, but 

 it is only the lower, never the upper portion of the stem that 

 they choose. The explanation given above will also account 

 for this fact. In the third place, he says, " The hardness of 

 the exterior of palm-stems cannot be owing to the pressure of 

 new matter from within outwards, but to some cause ana- 

 logous to the formation of heart-wood in exogens. Is there 

 any proof that such a cause is in operation ?" Before reply- 

 ing to this, I may observe, that the opinions of vegetable phy- 

 siologists are still unsettled regarding the formation of wood 

 in exogenous stems ; Lindley, and others, maintaining the 

 opinion of Du Petit Thouars, that the wood of a plant is 

 formed by the multitude of leaf-buds by which it is covered, 

 each of which may be considered a fixed embryo, having an 

 independent life and action — that by its elongation upwards 

 it forms new branches, and by its elongation downwards it 

 forms wood and bark ; — whilst DeCandolle, and most of the 

 French physiologists, explain its formation by the hypothesis, 

 that new layers are developed by pre-existing layers, which 

 are nourished by the descending juices formed in the leaves. 

 In palms, a longitudinal section of their stems, with the leaves 

 still attached to them, only requires to be seen to convince 

 the most sceptical that the ligneous substance of them is 

 formed by the leaves, and this affords another proof, at least 

 an analogical one, to the many which have already been given, 

 that the wood of exogens originates in the leaves. The only 

 difference between the formation of these two kinds of stems 

 seems to be, that in the exogenous tribes the woody fibre al- 

 ways remains between the bark and the last-formed layer of 

 wood ; while in the stems of palms the bundles of woody tis- 

 sue pass downwards and inwards to the interior of the stem, 

 then gradually downwards and outwards, and finally descend 

 parallel with the axis of the stem, through the previously 

 formed tissue of the same nature. 



Organ Mountains, Brazil, May 28, 1837. 



