6o 



HARDWICKE' S SCIENCE-GOSSIP. 



rich stores of fossil plants, which have been brought 

 to light chiefly through the labours of Messrs. 

 Butterworth, Nield, Earnshaw, and the late Mr. 

 Whittaker. Professor Williamson has frequently 

 alluded to the invaluable aid that he has received 

 from them, and of their untiring devotion to the 

 Cause of science. 



By a curious coincidence, my first acquaintance 

 with the fossil plant now under description, dates 

 from the first time that I met Mr. Butterworth. I 

 was geologising at Southowram Bank Top Coal Tit, 

 near Halifax, one Saturday afternoon, when the 

 unusual sound of a fresh hammer attracted my 

 attention. It proved to belong to Mr. Butterworth ; 

 mutual explanation took place, and among the 



Fig. 47. — Section of Lyginodendron Oldhamium (ma?. 12 diam 

 in Author's cabinet), a, central cellular pith; b, medullary cy 

 cylinder ; d, cortical bundles ; e, medullary rays ;/, inner bark 



"spoils" which we won on that occasion was a 

 good specimen of Lyginodendron Oldhamium. Since 

 then many a pleasant ramble have I enjoyed with 

 my Oldham friends, both in Yorkshire and Lancashire, 

 in search of fossil plants. 



Lyginodendron Oldhamium proves to be one of 

 the most common fossil plants found in our Halifax 

 district. My cabinet contains a large series of 

 sections of this plant which I have prepared from 

 specimens found in them. The one from which our 

 illustration has been taken has all its various tissues 

 in a beautiful state of preservation, and from which 

 we are enabled to learn a great deal about the 

 structure of the plant. 



On comparing a transverse section of Lyginoden- 

 dron with a similar one of Dadoxylon, we see at once 



that there is a very great difference in the structures- 

 of the two plants. We find that instead of the 

 simple, but very compact arrangement of the tissues 

 seen in the latter plant, there is a very complicated 

 state of arrangement of them in the former plant. 

 In Lyginodendron the tissues are not only more 

 varied in form, but the component cells and vessels 

 are also more variable in size and generally larger 

 than they are in Dadoxylon. 



A transverse section of Lyginodendron Oldhamium 

 (fig. 47) shows the usual tripartite division of the stem 

 into pith, woody cylinder, and bark. 



The pith is formed of two distinct zones, after the 

 manner of the pith of Lepidodendron Harcourtii, viz. 

 a central cellular medulla (a) formed of a very regular 

 hexagonal parenchyma, the cells of 

 which are larger than those composing 

 the pith in Dadoxylon. This central 

 cellular pith is surrounded by an in- 

 terrupted zone of vascular tissue, the 

 cells and vessels of which arebarred(^). 

 This zone is known as the " vascular 

 medullary cylinder." In very young 

 plants the central cellular pith is com- 

 pletely enclosed by the medullary 

 cylinder, but as the plant increased 

 in size, the latter began to break up> 

 and soon resolved itself into four 

 detached bundles, and the inter- 

 vening spaces became occupied by 

 the extension of the central cellular 

 pith. 



The woody cylinder (e) is formed 

 of vessels which are arranged in ra- 

 diating rows or laminas which are 

 separated from one another by true 

 medullary rays. In fig. 47 (/>) and in 

 young specimens generally, many of 

 these lamina; consist of a single row 

 of vessels, but other lamina; in the 

 same section have from two to six 

 rows of vessels, while in older plants 

 there are sometimes as many as 

 twelve or more rows of vessels in each lamina and 

 without intervening medullary rays. Generally speak- 

 ing, the vessels increase in size in passing from the 

 inner edge of the woody cylinder towards the peri- 

 phery, up to a certain limit, when they split up into 

 two ; those vessels which occur in single rows are 

 generally the largest, and they gradually decrease in, 

 size as the rows in each lamina increase in number. 



In longitudinal sections the vessels are seen to be 

 long tubes, and, as already stated, their walls are 

 reticulated, and not pitted as the vessels are in 

 Dadoxylon, or barred as in the Lepidodendroid 

 plants. The medullary rays (e) which bind the 

 laminae together, form nearly one-half of the ligneous 

 cylinder, and they are composed of elongated cells of 

 mural parenchyma, similar to those which occur in 



., from specimen 

 linder ; c, woody 

 ; g, fibrous layer. 



