6.1 8 



NA TURE 



[October 17, 1901 



evidence was derived from the microscopical examinalionof sub- 

 fossil wood, the occurrence of prehistoric and historic antiquities 

 preserved in the British Museum, in the Science and Arts 

 Museum in Dublin and elsewhere, and from the abundance of 

 place-names in England, Scotland and Ireland which owed 

 Iheir origin to the former existence of yew trees. 



On the distribution of certain forest trees in Scotland, as 

 shown by the investigation of post-glacial deposits, by W. N. 

 Niven. The author gave a summary of facts obtained from 

 various topographical books and other sources concerning the 

 distribution of the following trees : — Hawthorn, elder, common 

 ash, birch, alder, hazel, oak, willow, yew and fir, all of which, 

 with the exception of the ash, are considered natives of Scot- 

 land. The cones of the silver fir have been dug out of the peat 

 in Orkney, but this tree is not now indigenous to Scotland. 

 Several shrubs, including the juniper and raspberry, as well as 

 many flowering plants, have also laeen discovered. Mr. Niven 

 pointed out that there are few parts of Scotland, however tree- 

 less at the present day, that were not in remote, and even in 

 comparatively recent, times covered with woodlands. This is 

 also shown by the place-names. 



The evidence, which is obtained by the examination of the 

 various post-glacial deposits, indicates in a very clear manner 

 that the trees recorded should be considered truly indigenous 

 to Scotland, 



Prof. Potonie, of Berlin, read a paper on " Die Silur- und Culm- 

 Flora des Har7.es." On certain points in the structure of the seeds 

 Aelhiolfsia, Brongn. and Stephanos[<erninni. Brongn., by Prof 

 F. W. Oliver. Theauthorgavesomeaccount of the anatomy of the 

 fossil gymnosperm seed named by Brongniart Stephanospermtim 

 akenioides, and of another seed nearly allied to the foregoing 

 which he provisionally recognised as Ael/iiolesla subg/ohosa, 

 Brongn. Attention was drawn to the mantle of tracheal tissue 

 which invests the nucellus in both cases. The possible physio- 

 logical significance of this tissue was considered, and some 

 suggestions were offered as to the conditions which led to the 

 evolution of the seed in this group. The author expressed the 

 opinion that there was considerable probability that the seed 

 habit was at its origin a xerophilous adaptation. 



The structure and origin of jet, by A. C. Seward, F. R.S. 

 The author has recently examined several sections of Yorkshire 

 iet in the British Museum, which he believes demonstrate the 

 origin of this substance from the alteration of coniferous wood 

 and, in part at least, of wood of the Araucarian type. Sections 

 cut from specimens, which consist in part of petrified wood and 

 in part of jet, enable us to trace a gradual passage from well 

 preserved Araucarian wood to pure jet, which affords little or 

 no evidence of its ligneous origin. The conclusion arrived at is 

 that the Whitby jet owes its origin to the alteration of coniferous 

 wood. The fact that jet frequently occurs in the form of 

 flattened blocks of wood in all probability admits of the natural 

 explanation that the jet has been derived from the wood, the 

 form of which it has assumed, and not that the jet was formed 

 elsewhere and permeated the tissues of the wood as a fluid 

 bitumen. 



Mr. E. A. N. Arber described a number of specimens con- 

 tained in the Clarke collection of fossil plants from New South 

 Wales. The collection, which is now m the Geological Museum, 

 Cambridge, is noteworthy as being one of the earliest (1S39-44) 

 obtained from the continent of Australia. 



A chapter of plant evolution, by A. C. Seward, F. R.S. 

 The author described the chief features in the floras ranging from 

 the Rhi^tic to the Wealden ; he drew attention to the dominant 

 types which characterised this long succession of stages in the 

 earth's history and discussed the progress of plant-evolution from 

 the close of the Triassic period to the appearance of angiosperms 

 in rocks of Lower Cretaceous age. 



Morphology. — Cuticular structure of Euphorbia Abdelktiri, 

 by Prof. Bayley Balfour, F. R.S. Euphorbia Abdellmri \%, -s-n 

 interesting succulent plant which has been brought home from a 

 small island in the vicinity of Sokotra by the Ogilvie- Forbes 

 Expedition. The outer surface of the plant in the fresh condi- 

 tion appears to be covered with a crust which readily cracks off, 

 and on examination this is found to consist of a number of 

 prisms. At first sight these may be taken for some form of 

 mineral incrustation, but they are not of this nature, being 

 formed by the cuticle of the epidermal cells. This does not form 

 an uninterrupted layer over the epidermis, but the cuticle of each 

 itell is separable from that of the adjacent ones, and the prisms 

 are'merely blocks of cuticle, each one belonging to a single cell. 



NO. 1668, VOL. 64] 



This is a construction different from that which is ordinarily met 

 with in plants with a thick cuticular layer. 



Miss A. M. Clark described abnormal secondary thickening in 

 Ketidrickia IValkeri, a tropical epiphytic climbing shrub. The 

 anatomy of the young stem is typical of the family Melasto- 

 mace^. At an early stage numerous small patches and several 

 large wedge-shaped areas of thin-walled unlignified wood- 

 parenchyma are cut off from the inner side of the completely 

 circular cambium ring. Tylosis is of frequent occurrence, and 

 the tylosed cells may develop into sclerotic cells inside the vessels 

 and racheids. At a later stage, the unlignified wood-paren- 

 chyma cells at the central margin of the wedge area take upon 

 themselves new growth accompanied by cell-division. The 

 product of this new growth proceeds to split the axial woody 

 ring into a number of portions, with subsequent destruction of the 

 identity of the wood element.s. Later, the quiescent cambium 

 lying between the original internal phloem and the axial woody 

 ring takes upon itself new growth, and proceeds to lay down 

 xylem on the one side and phloem on the other. 



The histology of the sieve tubes o! Pin us, by A. W. Hill. — 

 The author's researches have proved that the results obtained by 

 Russow are, in the main, correct ; the mature sieve-plate is 

 traversed by groups of callus rods, which are interrupted at the 

 middle lamella by median nodules, and each callus rod contains 

 from three to seven stri.i;— or spots if examiried in surface-view — 

 which are strings of slime. The youngest sieve -plates or pit- 

 closing membranes, which could be examined, showed " con- 

 necting threads " like those in ordinary tissue ; but in the so- 

 called "boundary cells" — i.c'. the youngest thick-walled 

 sieve-tubes — a change takes place, namely, the appearance of 

 the callus. Callus first appears on one surface of the sieve-plate, 

 at the places where the groups of "connecting threads" occur, 

 and it gradually spreads as a rod along a group of the threads 

 to the middle lamella ; a similar change then takes place on the 

 other side of the lamella. The lamella itself, however, is not 

 convened into callus, but a refractive median nodule appears 

 separating the two portions of the callus rod. Accompanying 

 this change the protoplasmic threads become converted into 

 slime strings. The changes described were considered by the 

 author to be due to the action of ferments. 



Dr. Lotsy dealt with examples of heterogenesis in conifers. 

 The expressions heterogenesis (Korschinsky, " Flora," 1901), 

 mutation and spontaneous variation have practically the 

 same meaning, and are applied to phenomena which illus- 

 trate one method by which new species may be formed. 

 The author exhibited a specimen of Capsella Hcegeri, 

 given to him by Count Solms-Laubach, who recently described- 

 this species as a new form which appeared to have arisen 

 suddenly from Capsella bursa t>asloris (Bot. Zeitung, 1900). 

 Reference was made to Hugo de Vries' important publication 

 (" Mutationstheorie ") in which several new species are described 

 as having been formed as the result of sudden variations, 

 which were manifested during certain periods of spontaneous 

 variation. Dr. Lotsy drew attention to two genera of conifers — 

 Cupressus and Thuya — which he described as passing through 

 a period of spontaneous variation. Among a large number of 

 seedlings of Cupressus Lawsoniana two plants were raised which 

 exhibited marked differences — C. Lawsoniana Wisseti and C. 

 Lawsoniana lycopodioides, forms which would undoubtedly be 

 described as new species if their common origin were not known. 

 Thuya occidentalis Spaethi was also described as a new form 

 which had been pioduced as the result of sudden variation. 



Mr. John Paterson read a paper in which he dealt with the 

 biology and anatomy of Stellaria holostea and allied species. He 

 gave a brief comparative account of the anatomical structure 

 in SUllaria graniinea, S. media, S. glauca and other 

 Carjophyllacece. 



Mr. W. C. Worsdell submitted a paper on the morphology of 

 the ovule ; an historical sketch. The same author communicated 

 a note on the morphology of the "flowers" of Cephalolaxits, 

 containing an account of original observations on proliferated 

 inflorescences and flowers, which afforded evidence in support of 

 the foliolar theory of the ovule as put forward by Celakovsky. 



Physiology, iS^c. — Prof. Kny (Berlin) read a paper on Cor- 

 relation in the growth of roots and shoots, in which he dealt with 

 certain criticisms directed by Heering (Pringsheim's Jalirb., 

 1896) against a communication on the same subject published by 

 the author in i?,t)^(Annals Bot.). In the first paper the final 

 results, and not a detailed account of the experiments, were pub- 

 lished. Prof. Kny stated that his recent experiments had shown 



