250 



MORPHOLOGY. 



smaller loops are formed (fig. 163. B), 

 from whose circumference the vascular 

 bundles are given off for the leaf and 

 axillary bud, while the openings furnish 

 parenchyma for the formation of the 

 bud. The vascular bundles of every 

 newly developed internode stand in 

 immediate connection with, and are im- 

 mediate prolongations of, that portion of 

 the vascular bundle of the preceding 

 internode still capable of development, 

 and thus the cambium of the vascular 

 bundles forms a continuous net through 

 the stem and branches of the whole plant. 

 During the developments of the vascular 

 bundles of the stem, and those con- 

 nected with them, and belonging to an 

 axillary bud that grows into a branch, 

 the base of this branch becomes more 

 and more covered with newly formed 

 wood. We thus see the same condition 

 established as in the Monocotyledons : 

 an under lateral branch crosses all the 

 layers of wood passing to the upper 

 parts. The difference is merely, that in 

 the Dicotyledons they are portions of 

 the continuous mass of the progressively 

 developing vascular bundles ; while in 

 the case of Monocotyledons they are 

 discrete parts, new vascular bundles. 

 The wood is very various in its composition ( 26.). 



163 



B. With several concentric Kings of vascular Bundles. 



As far as I know, this condition is only met with in Piper (?) and 

 Pisonia ; and, perhaps, in a few of the Crassulacea, as in Crassula. 

 The separate vascular bundles continue to grow, and finally close into a 

 firm woody mass ; each, however, retains its own cambium, and likewise 

 a small portion of parenchyma, not perfectly dislodged : such, at any rate, 



163 JEsculus Hippocastanum, natural size. A, A longitudinal section of the end of a 

 twig some time before the bursting of the bud : a, the pith ; b, the wood ; c, the bark ; 

 d d, cicatrices of the uppermost leaves of the former year ; e e, the vascular bundles of 

 these leaves; ff, the axillary buds of these leaves, with their scales, and the vascular 

 bundles belonging to them ; g, terminal bud of the twig, ending in a blossoming 

 panicle ; h h, cicatrices of the lowest scales of the bud which have fallen off, together 

 with the axillary buds already visible : somewhat above this, the still-closed scales, 

 together with their vascular bundles ; i, medullary mass, which enters into the axillary 

 bud. B, Deeper part of a twig in the region of a leaf cicatrix, and a (severed) 

 axillary bud, the bark removed from it on the side turned towards the spectator : 

 i, crevice between the portions of the wood for the passage of the medulla into the 

 bud. Below this crevice there are seven others, lying in a semicircle, for the escape 

 of the vascular bundles destined for the leaf. 



