60 FORMATION OF WOOD. 



the stem, and when portions of bark are removed, a swelling takes 

 place above the parts where the injury has been inflicted, thus appa- 

 rently proving that the new matter is developed from above down- 

 wards. 



113. Gaudichaud endeavours to account for various anomalous 

 forms of stems (figs. 105-108), by considering them as depending on 

 the arrangement of the leaves, and on the mode in which the woody 

 fibres are sent down from them. Thus, the four secondary masses 

 surrounding the central one in the stem of Calycanthus floridus, are 

 traced to four vascular bundles from the leaves, penetrating the cellu- 

 lar tissue of the bark, distinct from the central wood and from each 

 other, except at the nodes, where the cross bundles unite them so as 

 to form a ring round the central mass. New fibres are formed on the 

 inner side of these bundles, and by degrees they assume a crescentic 

 shape, while the horns of the crescent ultimately unite on the outer 

 side (centrifugally), and enclose a portion of the bark, which thus forms 

 a kind of spurious excentric pith, with numerous woody layers on the 

 inside, and a smaller number on the outside. Again, in Brazilian 

 Sapindaceae (fig. 106), with five, seven, nine, or ten woody masses, 

 the same thing is said to occur, with this difference, that the pith of 

 each of the masses is derived from the original medullary centre, 

 portions of which are enclosed by the vascular bundles in a centripetal 

 manner, or from without, inwards. 



114. Treviranus states that the fibrous and vascular bundles de- 

 scending from the leaves, are destined in general to unite around a 

 common centre, but that they retain a certain degree of independence, 

 and may be developed separately in some instances, giving rise to 

 anomalous fasciculated stems. 



115. Gardner, from an examination of Brazilian Palms, adopts the 

 vertical theory, and Lindley also supports it. It is strongly opposed 

 by Schleiden, Mirbel, Naudrn, Henfrey, and others, who consider the 

 development of the vascular bundles, as proceeding from below up- 

 wards; in Dicotyledons, by peripherical production of woody and vas- 

 cular tissue from cambium cells ; and in Monocotyledons, by a definite 

 formation of woody and vascular bundles by means of terminal buds ; 

 the hardening of the stem depending on the interstitial changes which 

 take place afterwards in the woody fibres. 



116. A consideration of all the observations made on the formation 

 of woody stems, leads apparently to the conclusion, that there is an 

 ascending and descending axis in plants, and that each plant consists 

 of one or more individuals, or phytons (tpvrov, a plant), as they are 

 called by Gaudichaud and others, having both axes developed ; the 

 Exogenous stem being formed by the original formation of two oppo- 

 site phytons, the Endogenous by one : and that woody fibres are 

 produced from cells, which, in Exogens, are formed annually between 



