DENBIGHSHIRE GRITS, NEAR CORWEX, NORTH WALES. 



493 



the so-called Fucoidal remains are mere impressions, and many, if 

 not all, are trails or burrows of Annelida. 



The interest at first attached to these special remains was centred 

 in the hope that they were portions of terrestrial vegetation grow- 

 ing on a contiguous land surface during the deposition of the Den- 

 bighshire Grits. Xow, however, we have clear evidence that these 

 remains, to which we more especially refer, formed portions of a 

 colossal seaweed whose habit resembled that of the North-Pacific 

 species of the genus Nereocystis and the arborescent Lessonice, 

 and probably, as Air. Carruthers suggests, the Macrocystis pyrifera, 

 which attains the length of 700 feet. The arborescent Lessonice, 

 belonging to the natural order Laminariaceas, form large submarine 

 forests, the stems of which, when dry, resemble exogenous wood, 

 owing to a false exogenous growth. This pseudo-exogenous struc- 

 ture is well known in many of the Algse. Mr. Carruthers suggests 

 that in the arborescent Lessonice we have a near' approach to the 

 Devonian Nematophycus or Prototaxites. Many of the stems in 

 Lessonia measure a foot in diameter and 30 feet in length. The 

 Laminarice of our own shores exhibit a pseudo-exogenous growth ; 

 but, as is well known, the difference in growth between the Antarctic 

 Lessonia and the genus Laminaria consists in the " exogenous in- 

 crease in Laminaria being from below upwards, according to the 

 growth of the roots, while in the genus Lessonia the growth is 

 from above downwards, in proportion to the increase of the leaves"*. 

 Macrocystis belongs to the same natural order (Laminariacese), but 

 possesses a different habit. I may mention also D'Urvillea Harveyi, 

 Hook., another of the Laminariaceae, which possesses a stem-struc- 

 ture most closely resembling Nematophycus in the vermiform nature 

 of the cells or tubes, and their irregular semiparallel arrangement. 

 Dr. Hooker describes and figures this plant in his ' Antarctic Yoyage,' 

 vol. ii. t. 165-6 (fig. 2) ; a figure of the longitudinal structure of the 

 stem is given on the plate. The Corwen Nematopliycus is converted 

 into amorphous silex. This condition interferes with the microscopic 

 structure being readily made out, giving apparently false lines across 

 the tubes or cells ; and whether the spiral fibres are inside or out- 

 side the large tubes, or independent structures outside, I am unable 

 to say ; neither can Mr. Newton or myself clearly make out that the 

 so-called spiral fibres or concentric lines upon the tubes can be re- 

 solved into minute dots. His figure (fig. 4) is most carefully drawn ; 

 and one of the tubes containing the globular bodies is also delicately 

 and similarly lined. Fresh observations may enable us to determine 

 whether the spiral lines can be resolved into dots or not. The lon- 

 gitudinal and transverse sections prepared by Mr. Newton show 

 every feature described by Mr. Carruthers in his paper. The elon- 

 gated cylindrical cells, of two sizes, appear completely and irregu- 

 larly interwoven, as Mr. Carruthers well expresses it, into a kind of 



* Berkeley's Introduction to Cryptoganiic Botany, p. 57 ; Carruthers, 

 Monthly Microscopical Journal, 1872, pp. 170, 171. 



