W. Carruthers — Petrified Forest near Cairo. 309 



The chalcedony is more or less filled with minute bodies resembling 

 transverse hexagonal prisms of quartz ; but they are thin plates or 

 cavities penetrating the chalcedony in every direction. They have an 

 amorphous centre, and exhibit concentric lines of growth. They do 

 not affect the light differently from the substance in which they are 

 embedded, when examined by the polariscope. Newbold refers to a 

 specimen shown him by M. Linant, at Cairo, which had apparently 

 a somewhat similar structure, but it must have been on a much larger 

 scale, as he does not speak of using any magnifying power in ex- 

 amining it. He says it " had the hollow lined with a white chal- 

 cedony-like siliceous substance, full of small cells resembling those 

 of a honey-comb." (loc. cit. p. 353.) 



The stems, as determined by fiobert Brown, and confirmed by 

 Unger, belong to Angiospermatous dicotyledons, and are made up of 

 the tissues that enter into the composition of such plants. The 

 wood consists of slender prosenchytna, abundantly penetrated by 

 large ducts, which occur singly or arranged, two, three, or even more 

 together. The walls of the ducts are marked with small, regularly 

 arranged oval, or somewhat compressed hexagonal, reticulations. 

 Transverse diaphragms break up the ducts in well preserved speci- 

 mens into oblong compartments about twice as long as broad. The 

 medullary rays are abundant, and form a considerable proportion of 

 the stem. The concentric layers of wood are not so well defined as 

 one generally finds them in dicotyledonovxs stems, because of the 

 irregular manner in which the ducts occur throughout the year's 

 growth. In this respect they resemble the walnut rather than the 

 oak. 



The histological characters of the stem have been hitherto but 

 little used in systematic botany. A careful examination of numerous 

 specimens, and systematic arrangement of the results, would, no 

 doubt, throw much light on variations in stem- structure, associated 

 with variations in the structures of different plants. But as this has 

 not yet been done, I cannot go beyond E. Brown in saying that, 

 while these stems are dicotyledonous, they are not coniferous. 



The genus Nicolia was established by Unger in the second sup- 

 plement to Endlicher's "Genera Plantarum," (p. 102), and was 

 dedicated to William Nicol, who invented the process of slicing and 

 mounting fossil woods for microscopic examination ; and who thus 

 supplied the palaeontologist with the means of accurate investigation. 

 It may in passing be mentioned in connection with Nicol, that his 

 interesting collection of fossils is now deposited in the British 

 Museum, having formed part of the extensive collection of Alexander 

 Bryson, acquired some two years ago, after the death of that gentle- 

 man. 



The two species may be thus described, — 1. Nicolia JEgyptiaca 

 (Ung.), Endl. Gen. PI. Suppl. ii. p. 102, and Sitzungb. Math. Natur. 

 CI. Akad. Vien. vol. xxxiii. p. 214, pi. 1, figs. 1 and 2, Plate 

 XIV., Figs. 3 and 4. Wood cells in transverse section small, sub- 

 quadrangular, about one-tenth of the diameter of the large ducts. 

 Ducts roundish, singly, or two, three, and sometimes four, united 



