252 



MORPHOLOGY. 



167 



annual ring, so that a sharply 

 marked step is formed on 

 each side (fig. 166.); in an- 

 other species all that is 

 formed are four very thin, flat 

 plates, wholly separated (in 

 consequence of drying) from 

 the wood (fig. 167.). Gau- 

 dichaud* collected this stem, 

 and has drawn it, like the 

 rest, very rudely. Linkf says, 

 " In order to form a branch, 

 a portion of the wood accompanying the pith turns to the side, and, by 

 its increase, forms the branch. Sometimes the young branch goes out 

 from a three or four year-old stem or branch, separates the layers, and 

 thus makes its appearance on the surface. It is then seen as a wedge in 

 the wood of the old branch, which is larger or smaller according to the 

 modification of the branches. If the nodes stand in a cross [how can 

 the nodes stand in a cross ?] four wedges are seen standing opposed to 

 each other. Very large wedges of this kind are found in the stems of 

 the BignoniacecB from Rio Janeiro, such as I now have before me." If 

 Link here means the portions of stem mentioned, coming from Gaudi- 

 chaud, this is but an evidence of sad superficiality. Still more striking 

 is the cross-section of many climbers of the family of Sapindacea. A 

 hasty glance would lead us to imagine that we had here a cylinder of 

 wood surrounded with bark in which other stems or branches with their 

 bark had become blended in their growth (figs. 168,, 169.). A minute 

 observation, however, refutes this view at once from the absence of pith 

 in the exterior woody masses. It is especially peculiar here, that, as 

 appears from Gaudichaud's 

 is not continued 



TV \J \J\JL V JlltlOO\_-O J-U J.O ^OLJV^J.Cl>lAjr MV-'X-' dlACtJl A-lV^i V^j iii.tll/2 c*O 



audichaud's showy pictures, this separation of the wood 

 uniformly throughout the whole length of the stem, but 



* Loc. cit. tab. xviii. fig. 4. According to him, Bignonia capreolata would exhibit 

 the same phenomenon ; and this is to be found in some botanical gardens. A history 

 of the development of this peculiarity is very desirable. 



f Element. Phil. Bot. ed. 2. vol. i. p. 273. 



They consist of parenchyma, and concentrically arranged bundles of very much thickened 

 gold-coloured liber-cells : the wood exhibits no annual rings. The medullary rays are 

 present in the wood-wedges, which form, as it were, the continuation of the interposed 

 portions of the bark ; but they are far less conspicuous. The wood, besides the wood- 

 cells, contain also some parenchymatous cellular tissue. 



166 The tissue of the wedges (a, a), passing in by step-like gradations from the bark, 

 is very remarkable. It exhibits distinct medullary rays, which are continued from it 

 to the pith, whilst they are very indistinct in the rest of the wood. Between the me- 

 dullary rays there are bundles of thick-walled and densely porous parenchymatous cells 

 (similar to many liber-cells ; as, for instance, in Cereus), and a great number of very 

 broad, thin- walled, scarcely perceptible, porous cells, whose steeply ascending transverse 

 septa exhibit strikingly evident reticulated fibres, the interstices of which are filled with 

 a membrane, closely beset with fine pores. 



167 The narrow intervening pieces of bark (a a) consist here of but little cellular 

 tissue, and a greatly preponderating quantity of liber. Annual rings are not distinctly 

 traceable in the wood. The wood consists principally of parenchyma, having only thin 

 bundles of wood-cells. 



