FOSSIL PLANTS OF THE COAL-MEASURES. 323 



and habit of the plant. To quote WiUiamson and Scott's words — 

 " We must, therefore, picture Lyi/inodendnm to ourselves as having 

 a tall, upright stem rising to a height of several feet, and bearing 

 somewhat remote, spirally arranged, highly compound fern-leaves. 

 The base of the stem, where the adventitious roots were given oflf, 

 must have been buried for some depth in the earth or mud." The 

 centre of the stem was occupied by a parenchymatous pith con- 

 tainiug characteristic "nests" of sclerous cells. At the periphery 

 of this medullary tissue, occurs a ring of detached strands of 

 primary xylem, each consisting of spiral, scalariform and pitted 

 trachea^ with a small amount of parenchyma. External to these 

 primary groups is a ring of secondary wood, made up of radially 

 arranged pitted trache;e and medullary rays ; the phloem consists 

 of parenchyma and sieve-tube-like elements, and, like the xylem, 

 is ti'aversed by medullary ray cells. In some specimens patches of 

 primary phloem have been recognized external to the secondary 

 phloem, and between the secondary xylem and phloem a well- 

 marked cambium is shown in wonderful perfection in some of the 

 drawings accompanying the paper. Passing beyond the vascular 

 tissue, we find a pericycle which at an early stage in the growth of 

 the plant gave rise to a periderm. The cortex proper consists 

 internally of parenchymatous tissue containing nests of sclerous 

 cells ; external to this, alternating radial bands of parenchyma and 

 sclerenchyma constitute the exceedingly characteristic outer cortex 

 of the stem. Secretory sacs are abundant in the pith, medullary 

 rays, and inner cortex. Leaf-trace bundles are constantly seen in 

 transverse sections on their way out to the petioles. Those met 

 with in the secondary xylem, are in the form of single groups of 

 primary xylem with a fan-shaped group of secondary trachea) on 

 the external face of the primary strand. If such a leaf- trace bundle 

 be followed to the petiole, it is found to pass through five internodes 

 before entering the pericycle ; during this part of its course it loses 

 its secondary xylem, and begins to divide into two bundles. Finally 

 the twin bundles pass gradually outwards until they enter the 

 petiole. The primary xylem strands of the stem have been shown 

 to be the downward prolongations of the leaf-traces ; hence the 

 bundle system of Lijginodendron is essentially a leaf- trace system. 



The most important points with regard to the detailed structure 

 of the primary bundles are (1), their collateral nature, and (2), the 

 occurrence of the protoxylem in an internal position in each 

 primary xylem-strand. In short, the structure of each primary 

 bundle agrees very closely with that of the foliar bundles in recent 

 Gycads. The secondary wood also exhibits a striking resemblance 

 to the secondary wood of cycadean stems. 



The petioles of this genus are of the type previously known as 

 llachiopteris aspera Will., and the pinnules are clearly such as 

 conform to the characters of a typical S/ihenopieris. It is a fact of 

 importance that the collateral leaf-trace in the stem assumes a 

 concentric structure as it passes into the petiole. Finally, it is 

 now perfectly clear that Williamson's Kaloxylon Hookeri is the 

 adventitious root of Lyginodendron. 



