November. 1910. 



KNOWLEDGE. 



449 



puzzling maze of cross-affinities. The conflicting lines of 

 resemblance among Conifers probably point to a more ancient 

 lineage for all the families than has hitherto been realised. 



TRYPANOSOME-LIKE P.4R.A.SITES IX PL.\XTS.— 

 It has recently been discovered that parasitic flagellates, 

 resembling the trypanosomes which occur so widely in animals, 

 and which cause malaria and other diseases in man, are found 

 also in plants. The presence of a trypanosome-like parasite 

 in plants was first made known by Lafont (Coinptes rendus, 

 1909-1910), who found these organisms in the milky juice 

 (latex) of a spurge (Euphorbia) from Mauritius. The 

 discovery has been confirmed by Donovan iLancct, 1909) in 

 the same species of spurge, growing in Madras, and in his 

 second paper Lafont gives a full account of the organism, 

 which he has now found in three species of EiipJtorbia. The 

 infected plants show marked signs of malnutrition, and finally 

 drop their leaves and die. Lafont found that injection of the 

 parasites into the blood of small animals produced no infection, 

 though some of the animals died " from unknown causes." 

 The further development of this remarkable addition to our 

 knowledge of plant diseases will be awaited with great interest. 



THE WOODL.AXDS OE EXGLAND.— An ecological 

 memoir of great interest has recently appeared in the Xeic- 

 Pliytologist under this title. It represents the first satisfactory 

 attempt to give a bird's-eye view of English Woodlands as a 

 whole, and is based on a paper read by Tansley at the Dublin 

 meeting of the British Association in 1908. The authors 

 (Tansley. Moss, and Rankin), after discussing the general 

 characters of British Woodlands, the relations of climate and 

 soil, and so on. proceed to the classification of the Woodlands, 

 of which they recognise three main series : — 



I. The Alder-Willow Series. This is a lowland type 

 occurring on very wet soils, and is characteristic of low-lying 

 alluvial districts, as along the banks of the slow streams of the 

 New Eorest, the remoter valleys and lowland peat-moors of 

 the North of England, and in the fens of Norfolk. The woods 

 of this series at present existing probably represent merely 

 fragments of a once e.\tensi\'e development, by now greatly 

 reduced in consequence of drainage and culti\ation. At least 

 two plant associations occur in it, e.g.. the Carrs of Xorfolk. 

 fed by alkaline and calcareous waters, harbour several woody 

 species characteristic of chalky and limestone soils, such as 

 Rhaiiiiiiis catharticiis and Vibitnitiin Laiitatin. while in 

 the Alder- Willow thickets occurring on soils fed with neutral or 

 acidic waters, calcicole species are absent. From this lowland 

 type two great systems occur, the distribution of which follows, 

 in the main, two chief classes of soil, siliceous and calcareous. 



II. Oak and Birch Series. The woods in this series occur 

 on all the "siliceous" (/.c, non-calcareousi soils, ranging from 

 the stiffest clays to sand and gra\el, and deri\ed from rocks of 

 various ages. Within this series three associations occur, but 

 more or less merging into one another. 1.4) An Oakwood 

 Association, by far the most widely distributed of 

 British W'oodlands. The dominant tree is Uiierciis robitr 

 (^O. pcdnnculata\. Owing to the great variety of soils on 

 which the oak is dominant, the associated trees and especially 

 the ground vegetation, show a wide range, and two groups of 

 associations are distinguished — (a) Damp Oakicoods on clays 

 and loams of the London Clay, the Gault. the Weald Clay, 

 and so on. in the south of England : these are connected by 

 every gradation with (6 1 the Dry Oakic-oods.ioimdon coarsely- 

 grained, siliceous, shallow soils of the Palaeozoic and igneous 

 rocks of the west and north of England. In these woods 

 Q. sessiliflora is usually dominant, but with a varying 

 .admixture of O. robtir. iB) The Oakbirch-hcath association 

 is a type characterised by the presence in the ground vegeta- 

 tion of bilberry, hair grass and ling. Such woods cover wide 

 areas in Kent, Surrey, Sussex, and locally as far north as 

 Cheshire and Xottingham. This wood is probably a stage in 

 the degeneration of oak forest to heath land, similar to that 

 described by Graebner in the great heaths of the north-west 

 German plain. In the hilly districts of the north of England, 

 the woods on non-calcareous soils are dominated by O. 

 sessiliflora, but this tree becomes rare above 1.000 feet, and 

 owing to cUmatic influences tends to be replaced by (C) The 



Birchicood Association, in which the woods are floristically 

 \-ery similar to the Oakwoods, but the ecological differences 

 appear in the rearrangement of the dominant members of the 

 two associations. Judging from the remains of Scots Pine 

 in the peat of the Pennines, this tree was doubtless a 

 constituent, but probably not an abundant one, of the 

 primitive Pennine birch forests. 



III. The Beech and Ash Series is sharply marked oft" from 

 the two preceding series. These woods are found on 

 calcareous soils (such as marl, chalk, limestone) where the 

 lime content of the soil is high. Here three associations are 

 distinguished — (A) an Ash-BeccJiwood Association ; (B) an 

 AsliK-ood .Association ; IC) a. Beecli\i.ood Association. (A) 

 and (B) are the characteristic w-oodland types on all highly 

 calcareous soils, e.xcept those of the south-east of England, 

 where the beech is dominant on the chalk. The area of 

 natural and semi-natural beechwoods appears to have a 

 western extension on the Inferior Oolite of the Cotswold, but 

 for the most part it does not extend north-westwards of the 

 chalk escarpment. 



For each association in these series, lists are given of the 

 subordinate woody species, as well as the characteristic species 

 of the ground vegetation. 



The foregoing summary of this most useful memoir is based 

 upon that given in the Naturalist by Ur. Woodhead, well 

 known for his own valuable work in Ecolog\'. Readers 

 interested in the subject should obtain the memoir itself, 

 which has been separately issued as a " Nexv Pliytologist 

 Reprint " and can be purchased at a shilUng (by post. Is. Id.) 

 from the Editor, " A'cxc Pliytologist." Botany School, Cam- 

 bridge, or from Dr. W. G. Smith. Agricultural College, George 

 Square, Edinburgh. 



CHEMISTRY. 



By C. .\iNS\voRTH Mitchell. H..\. (O.xon)., F.I.C. 



METALLIC RADIUM.— Until recently radium has only 

 been known in the form of salts, such as the chloride or 

 bromide, but Madame Curie and M. A. Debierne ha\-e at 

 length succeeded in separating a small quantity of the 

 elementary substance, and give an account of its properties in 

 the Coiiiptes Rcndtis (Vol. cli. 523). 



A licjuid amalgam of radium was first prepared by electro- 

 lysing a solution of radium chloride by means of a cathode of 

 metallic mercury and an anode of an alloy of platinum and 

 iridium. This amalgam was rapidK- dried and placed in an 

 iron boat, which was heated in a quartz tube containing an 

 atmosphere of hydrogen, the pressure of which was maintained 

 at a point abo\e the pressure of mercury \apour at the 

 temperatures of the experiment. After the bulk of the mercury 

 had distilled the temperature was gradually increased, until at 

 about 700° C. the remainder of the mercury was expelled, and 

 the volatilisation point of the radium was reached. The residue 

 left in the iron boat was a bright white metal, which melted at 

 700" C. and at higher temperatures volatiUsed and attacked the 

 quartz tube. 



The radium thus obtained rapidly blackened on exposure to 

 air, a nitride apparently being formed. It also decomposed 

 water, being itself for the most part dissoKed in the process. 

 Like its salts it was radio-active. 



AN ANCIENT GLASS MIRROR.— The current issue of 

 the Monatshcft.Clicni.Wol xxxi.p. 781 ) contains a description 

 by Messrs. Wafert and Milkauz of an old Roman mirror that 

 was discovered in the ancient burial ground at Laibach, and 

 is believed to date back to the second or third century .\.D. 

 It was a slightly convex glass plate fitted into an indented 

 and ornamented leaden ring, and from its appearance under 

 the microscope and the results of chemical examination, the 

 mirror had probably been formed by attaching lead foil to the 

 back of the thin glass by means of some balsam. In the 

 course of centuries the balsam had become resinified and had 

 combined with the lead to form a resinate. The bulk of the 

 lead of the foil had been converted into red lead (Pb.i04), 

 whereas the lead of the frame and on the back was largely in 

 the form of basic lead carbonate. 



