62 



IIARDWICKE'S SCIENCE-GOSSIP. 



nothing remains, save the narrow outlines of the 

 edges, which cause these sections to look very like 

 tangential sections of Lyginodendron. But upon 

 comparing them under the microscope, the difference 

 between them is seen at once. The large rhomboidal 

 spaces between the fibrous bands are filled with 

 cellular tissue, which varies considerably in form even 

 in the same plant. 



In the transverse section from which our illustration 

 is taken, this tissue takes the form of long oblong 

 cells, which in some cases stretch across the spaces 

 between the fibrous bands, in others they are trailed 

 about in a very curious manner, which is very pro- 

 bably due to shrinkage during or before fossilisa- 

 tion. They gradually decrease in size, as they ap- 

 proach the regular tissues of the inner bark. There 

 is yet another interesting feature in connection with 

 the bark. 



Placed amid the cellular tissues of the inner bark 

 are four pairs of vascular bundles (d), formed of 

 similar tissues as those composing the vascular me- 

 dullary cylinder. These bundles form an interesting, 

 and at the same time a most characteristic feature, in 

 all transverse sections of Lyginodendron Oldhamium. 

 In longitudinal sections they are not so conspicuous, 

 on account of their component vessels being reticu- 

 lated in the same way as those forming the con- 

 tiguous ligneous zone, so that they appear to be 

 merely its outer edge. 



The presence of these bundles explains a curious 

 feature which is observable in most transverse sections 

 of this plant, and which was for a long time a puzzle 

 to me, and that is, the undulating outline presented 

 by the ligneous cylinder. 



At the first glance it might appear, as it did to me, 

 that these undulations were due to pressure, but such 

 is not the case, as they occur in specimens which do 

 not appear to have been at all compressed, and 

 which have their tissues well preserved. These cor- 

 tical bundles are placed in the hollows where the 

 undulations curve inwards, while those of the medulla 

 are placed where they curve outwards. It appears 

 very probable, as was suggested by Professor William- 

 son, that the two sets of bundles acted as stays or 

 buttresses to strengthen the somewhat lax tissues of 

 the plant. The great majority of specimens of this 

 genus shew no signs of either branches or foliage, 

 for the cortical bundles do not appear to have any 

 connection with either leaves or branches. There are 

 other bundles of tissue in the bark which may have 

 had some connection with either leaves or branches. 

 Some of my specimens show branches or fronds being 

 given off from the bark. There are other petiolar bun- 

 dles which originate either in the ligneous zone or 

 medullary cylinder, but which, in many cases, appear 

 to have terminated at[the outer surface of the bark, and 

 most probably were connected with leaves or cones or 

 other deciduous appendages. These facts render it pro- 

 bable that the stem may have had a crown of fern-like 



fronds ; there are also other facts which point to the 

 affinity of Lyginodendron with the tree-ferns. But 

 on the other hand, in its double pith and woody 

 cylinders, it is more allied to the Lycopodiaceae, as 

 represented by the Lepidodendroid plants. It is one 

 of the many coal plants, of which it may be said 

 that we have yet to learn a great deal more about them 

 before this can be placed in its proper position in the 

 vegetable kingdom, and also one in which we may 

 perhaps learn something about the great question 

 of the evolution of the fossil plants of the coal- 

 measures. 



The chief object which I have in view in writing 

 these papers is,' that by the aid of our studies among 

 the fossil plants found in our coal-ball nodules more 

 light may be thrown on the history of our ordinary 

 fossil plants, and especially on those forms the history 

 of which is very obscure, so as to still further increase 

 the growing interest taken in them. 



My cabinet contains a series of peculiar impressions 

 of fossil plants with which I have long been familiar, 

 but which I was unable to make anything of as to 

 the kind of plant to which they had belonged. 



But after reading the above memoir on Lygino- 

 dendron Oldhamhim, and becoming practically ac- 

 quainted with the structure of the peculiar cortical 

 fibrous layer as seen in tangential and transverse 

 sections, a flood of light was thrown on these hitherto 

 unknown fossil impressions. 



In the sandstone rocks of the millstone grit series, 

 as well as in those of the coal-measures, we frequently 

 find fragments of sandstone casts which are character- 

 ised by the possession of a series of raised ridges 

 and corresponding depressions, which ascend the stem 

 in a somewhat spiral manner, nearly after the manner 

 of the leaf-scars of the Lepidodendroid plants. These 

 ridges and furrows vary considerably in length, accord- 

 ing to the size of the plant, and very probably these 

 variations also sometimes indicate different species. 

 In some specimens the ridges are fully four inches in 

 length, while in others they are not more than half 

 an inch in length. They also vary considerably in 

 height and form : some of them are smooth and 

 rounded ; others stand up half an inch above the 

 surface of the plant, ending in a sharp edge ; others 

 again are rounded and striated. The most beautiful 

 specimens are, however, found in the ironstones of 

 the coal measures, as is usually the case w ith most of 

 the ordinary fossil plants. Fig. 49 is taken from one 

 of these ironstone fossils. 



Fossil collectors generally regard them as the 

 impressions of Lepidodendroid plants, to which they 

 bear a close resemblance. But this is one of those 

 cases which not unfrequently occur among fossil 

 plants, in which the ordinary impressions and casts 

 convey but a faint idea of the real form of the 

 original plant when growing in its native soil. These 

 singular fossils are the impressions of the fibrous 

 layer (fig. 47, g) in the bark of Lyginodendron, and, of 



