0)1 the Fossil Plants of the Coal-measures. 137 



numerous and intervene between all the numerous radiating lamince 

 of vessels that constitute the larger wedges of woody tissue. The 

 vessels going to the rootlets are not given off from the pith, as 

 Goeppert supposed, but from the sides of the woody wedges bounding 

 the upper part of the several large lenticular medullary rays, those 

 of the lower portion of the ray taking no part in the constitution 

 of the vascular bundles. The vessels of the region in question 

 descend vertically and parallel to each other until they come into con- 

 tact with the medullary ray, when they are suddenly deflected, in large 

 numbers, in an outward direction, and nearly at right angles to 

 their previous course, to reach the rootlets. But only a small number 

 reach their destination, the great majority of the deflected vessels 

 terminating in the woody zone. A very thick bark surrounds the 

 woody zone. Immediately in contact with the latter it consists of 

 a thin layer of delicate vertically elongated cellular tissue, in which 

 the mural tissues of the outer extremities of the medullary rays 

 become merged. Externally to this structure is a thick parenchyma, 

 which quickly assumes a more or less prosenchymatous form and 

 becomes arranged in thin radiating lamina) as it extends outwards. 

 The epidermal layer consists of cellular parenchyma with vertically 

 elongated cells at its inner surface, which feebly represents the 

 bast-layer of the other forms of Lepidodendroid plants. The root- 

 lets consist of an outer layer of parenchyma, derived from the 

 epidermal parenchyma. Within this is a cylindrical space, the 

 tissue of which has always disappeared. In the centre is a bundle 

 of vessels surrounded by a cylinder of very delicate cellular tissue, 

 prolonged either from one of the medullary rays or from the delicate 

 innermost layer of the bark, because it always accompanies the 

 vessels in their progress outwards through the middle and outer barks. 



The facts of which the preceding is a summary lead to the con- 

 clusion that all the forms of plants described are but modifications of 

 the Lepidodendroid type. The leaf-scars of the specimens so common 

 in the coal-shales represent tangential sections of the petioles of leaves 

 when such sections are made close to the epidermal layer. The thin 

 film of coal of which these leaf-scars consist, in specimens found both 

 in sandstone and in shale, does not represent the entire bark, as 

 generally thought, and as is implied in the term "decorticated" 

 usually applied to them, but is derived from the epidermal layer. 

 In such specimens all the more central axial structures (viz. the 

 medulla, the wood, and the thick layer of true bark) have disap- 

 peared through decay, having been either destroyed or in some 

 instances detached and floated out ; the bast-layer of the epiderm 

 has arrested the destruction of the entire cylinder, and formed the 

 mould into which inorganic materials have been introduced. On 

 the other hand, the woody cylinder is the part most frequently pre- 

 served in Stiginaria, doubtless because, being subterranean, it was 

 protected against the atmospheric action which destroyed so much 

 of the stem. 



It is evident that all these Lepidodendroid and Sigillarian plants 

 must be included in one common family, and that the separation 



Ann.&Mag.N.Uist, ^tw^l YcJ,\i\\, iO 



