Dr. F. A. Bather — Prof. Nathorsfs Studies of Fossil Plants. 455 



could be studied under the microscope without more ado. " The 

 whole process," he writes, " of obtaining these natural microscope- 

 preparations of the epidermis of fossil plants consists in loosening 

 them from the clay under water with a spatula, mechanically washing 

 the adherent clay from the membrane, and then enclosing the latter 

 in hot, fluid Canada balsam between two glass plates." As a rule, 

 however, more elaborate methods are needed both to obtain the 

 cuticle and to render it fit for study. 



August Schenk, in his memoir on ''Die fossile Flora der 

 Grenzschichten des Keupers und Lias Frankens " (Wiesbaden, 1867), 

 was probably the first to make any considerable series of such 

 preparations, as well as of the spores of various ferns. Similar 

 researches have been made by R. Zeiller, who, in his "Observations 

 sur quelques cuticules fossiles" (1882, Ann. Sci. Nat,, ser. vi,_Botan., 

 vol. xiii, pp. 217-38), explained certain methods of treating the 

 cuticle chemically. The cuticle of most plants, though insoluble in 

 cold concentrated sulphuric acid, is dissolved in hot nitric acid, being 

 changed by oxidation into suberic acid; it is also saponified and 

 dissolved by boiling in potash. Fossil cuticles resist concentrated 

 sulphuric acid even when boiling, and are dissolved in nitric acid only 

 by prolonged boiling, the residue giving the usual reaction for suberic 

 acid ; they are not acted on by potash. As first observed in the 

 Papierkohle, the carbonaceous matter separating the membranes is not 

 carbon but ulmic acid, and this is soluble in slightly warmed ammonia 

 or potash. Truly carbonised matter may be attacked by chlorine 

 water (*eau de chlore') or by nitric acid, which oxidises it into 

 ulmic acid soluble in alkalis. 



Methods based on the foregoing facts have been employed by 

 Zeiller and subsequent authors in this country and elsewhere, but 

 have recently been improved by Dr. Hjalmar Miiller, working under 

 the direction of Professor A. G. Nathorst. A full account of them, 

 with examples of their use, is given in some valuable memoirs 

 recently published by Professor Nathorst,^ and the interest taken in 

 his coUodium-method - suggests that some abstract of his present 

 remarks may also prove welcome. 



In studying carbonised leaves, the usual method has been to bleach 

 them with chlorate of potash and nitric acid ^ ; now it is found 

 preferable generally to use the aqueous solution of potassium hypo- 

 chlorite known as Eau de Javelle. This, being slower and gentler in 

 its action, enables one to obtain larger portions of the leaf-cuticle 

 unharmed. Sometimes, it is true, the material is not appreciably 

 attacked by the Eau de Javelle, and recourse must then be had to the 

 older method. 



1 A. G. Nathorst, 1908, " Palaobotanische Mitteilungen, Nos. 3-6 " : K. Svenska 

 Vet.-Akad. Handl., xliii, 3 and 6. No. 3, " Lijcostrohus Scotti, eine grosse 

 Sporophyllahre aus den ratischen Ablagerungen Sehonens " ; No. 4, "Ueber die 

 Untersuchung kutinisierter fossiler Pflanzenteile " ; No. 5, " Ueber Nathorstia 

 Heer " ; No. 6, " AnthoUthus Zeilleri, n.sp., mitnocb erhaltenen PoUenkornem aus 

 den rhatischen Ablagerungen Sehonens." In all, 46 pages, 6 plates. 



2 See Geol. Mag., Oct., 1907, pp. 437-40. 



3 See, for instance, A. C. Seward, " Fossil Plants," 1898, p. 75, at bottom. 



