154 



THE VASCULAR SYSTEM OF THE AXIS 



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certain Superficiales, and in Matonia the ontogeny has been worked out by 

 Tansley and Lulham. The mature rhizome of Matonia shows in the most 

 complex cases three concentric rings embedded in well-ventilated paren- 

 chyma, and each having the typical solenostelic structure (Fig. 148). If 

 sections be taken transversely at a node, 

 the connections with the leaf-trace are 

 seen. Fig. 148 shows this for three succes- 

 sive ages. The youngest {A ) demonstrates 

 the small leaf-gap; the older {B, C) show 

 how the curved leaf-trace is directly con- 

 tinuous with the outer and middle rings 

 at the node. There may also be a con- 

 nection with the inner ring; but this occurs 

 at some little distance from the actual 

 node. The result is that the whole system 

 is connected, while there is also communi- 

 cation through the leaf-gaps between the 

 inner and outer parenchymatous tracts in 

 which the cylinders are embedded. The 

 ontogeny shows how this structure is 

 arrived at. The young axis contains at 

 first a slender protostele, which soon ex- 

 pands, and phloem • appears centrally in 

 it ; but there is as yet no true leaf-gap. 

 The stele soon widens into a solenostele 

 with internal endodermis surrounding a 

 central pith. Meanwhile at the nodes a 

 ridge of vascular tissue projects internally, 

 and, becoming detached as a separate rod, 

 it is continued forwards into the internode 

 further and further at successive nodes, 

 till that of one node eventually connects 

 with that of the next node (Fig. 148, A). 

 A continuous central strand is thus pro- 

 duced, which is connected at the nodes 

 with the outer cylinder. The process thus 

 described may then be repeated in this 

 central strand : it also becomes cylindrical, forming a second vascular ring 

 which is still connected at the nodes with the foliar system (Fig. 148, B). 

 A fresh strand may then originate from it: this in turn becomes cylindrical 

 in the largest rhizomes, but it still maintains its connection with the middle 

 and outer rings in the neighbourhood of the nodes (Fig. 148, C). The whole 



Fig. 148. jUaio^impect/^iafajdrsLw'mgsh-om 

 wax models of the stelar system. A — from 

 a young stem showing a node. j9 = from 

 an older stem, showing a node as seen 

 from behind. C= still older node seen 

 from the front. (A x 25; B x 12; Cxio.) 

 (After Tansley and Lulham.) 



