6l2 



NA TURE 



[October i8, 1900 



been indehiscent, and presents close analogies with a true seed. 

 In a male strobilus, probably of the same species as the speci- 

 mens above described, the microsporangia were found to be pro- 

 vided with integuments, resembling those of the megasporangia, 

 but more widely open. 



It is proposed to give the generic name Lepidocarpon to this 

 Lepidostroboid fructification. 



The primary structure of certain Palaeozoic stems referred to 

 Araucarioxylon, by D. H. Scott, F.R.S. The Palaeozoic forms 

 oi Araticarioxylon have been shown to belong in most casesto 

 the stems of the extinct Gymnospermous order Cordaiteae, which 

 was in some respects intermediate between Cycadales and 

 Coniferae. The Cordaitean stems hitherto investigated resemble 

 Coniferae in the development of their wood, for the spiral first- 

 fortrftd tracheides are found in contact with the pith, the whole 

 of the wood, primary as well as secondary, having thus been 

 developed in centrifugal order. The specimens of Lower 

 Carboniferous age now illustrated are peculiar in possessing dis- 

 tinct strands of primary wood in the pith. In one, Araticari- 

 oxylon fascicular e, sp. nov., the pith is small, but the primary 

 strands of xylem are of large size, attaining their maximum 

 diameter when about to pass out towards a leaf. Their structure 

 is mesarch, and they closely resemble the corresponding strands 

 in Lyginodendron Oldhainium. The secondary wood has 

 narrow medullary rays, and resembles that of an araucarian 

 Conifer. The other species is identical with Araucarioxylon 

 antiquum of Witham. The interest of the two species (de- 

 scribed from specimens in Mr. Kidston's collection) consists in 

 their affording a link between certain of the Cycadofilices and 

 the Cordaite^. 



On the structure and affinities of Dipteris conjugata, with 

 notes on the geological history of the Dipteridinae, by A. C. 

 Seward. F.R S., and Elizabeth Dale. The genus Dipteris is 

 represented by four recent species : D. conjugata, Reinw. 

 [= Polypodium {Dipteris) Horsfieldti, R. Br.], D. Wallichii, 

 R. Br., D. Lobbiaiia, Hk., and D. qtcinquefurcata, Baker. 

 Among Mesozoic ferns the genera Protorhtpis, Dictydphylluin 

 and Camptopteris afford examples of extinct types closely allied 

 to Dipteris, and widely spread geographically during the Jurassic 

 epoch. 



The sporangial characters of Dipteris do not conform precisely 

 to those typical of the Polypodiaceas, and the anatomical 

 features afford additional evidence in favour of placing Dipteris 

 in a special subdivision of the leptosporangiate ferns. 



The paper dealt with the structure of the stem, which 

 possesses a single annular stele, the roots, leaves and sporangia 

 of Dipteris conjugata, the comparison of the anatomical 

 •features with those of the Cyatheaceae and other ferns, and 

 concluded with an account of the geological and geographic il 

 range of such fossil ferns as may reasonably be placed in the 

 family Dipteridinae. 



On the structure of the stem of Angiopleris evecta, Hoffm., 

 by R. F. Shove, Girton College, Cambridge. This paper 

 dealt with the anatomy of the stem and roots of a plant of 

 Angiopteris evecta from Ceylon. 



The steles of the stem are both mesarch and endarch in 

 Structure, but the protoxylem groups occupy for the most part 

 a peripheral position. The earliest protoxylem appears along 

 the inner edge of the steles, while the protophloem arises on 

 the outer edge of each stele as a discontinuous arc of small and 

 rather thick-walled elements. This arc of protophloem is never 

 completed round the stele, but the next stage in the develop- 

 ment of the tissues after the appearance of the protoxylem is 

 the differentiation of large sieve-tubes external to the proto- 

 phloem. 



The conducting tissues of Bryophytes, by A. G. Tansley. 

 The most important part of our present knowledge of these 

 tissues is due to Haberlandt, who, in the Polytrichaceae, dis- 

 tinguished a hadroin [hydrom) or water-conducting system from 

 a leptom system, conducting plastic, especially nitrogenous 

 substances. 



In the present investigation the lignified strand of prosen- 

 chyma in the thallus of certain Liverworts was shown to be 

 a hydrom strand, and its development was considered to be 

 correlated to some extent with the localisation of the absorptive 

 region of the thallus. 



The rhizome of four species of Polytrichum was investigated, 

 and was found to possess the distribution of tissues characteristic 

 of the root of a vascular plant. The transition to the structure 

 of the aerial stem was followed, and some new points in the 



NO. 1 616, VOL. 62] 



structure and course of the leaf-traces were observed ; new light 

 was thrown also on the constitution of the Polytrichaceous 

 stele, which is thought to consist of two regions distinct in 

 function and by descent. An attempt was made to trace out the 

 course of evolution of these conducting tissues in the Bryophytic 

 series. 



The origin of modern Cycads, by W. C. Worsdell. The 

 author's conclusion is that the Cycads are descended directly 

 from some cycado-filicinean type possessing the structure exhibited 

 especially by such forms as the MeduUoseae and Lyginodendreae, 

 the chief point being that the fo//i2/i?ra//f-constructed one or 

 more vascular cylinders of modern cycads have been derived 

 from one or more concentrically-constructed cylinders of some 

 cycado-filicinean form. Those characters in the modern plants 

 which approximate most nearly to the primitive ancestral type 

 are found in those parts of the plant where they would most 

 naturally be expected, viz. : — ^The axial organs : the primary node 

 or transitional region between stem and root, and the flowering 

 axis; the y^/zar organs : the cotyledon, the sforopkyll, a.nd the 

 integument of the sporangium. The author discussed the evi- 

 dence derived from an anatomical study of recent cycads, and 

 dealt with certain fossil types which he regarded as supporting 

 his conclusions. 



Cytology, &c. 



On the osmotic properties and their causes in the living plant 

 and animal cell, by Prof. Overton. A ^ery great number of 

 experiments on the permeability or the living protoplasm of plant 

 and animal cells has led to the conclusion that the general 

 osmotic properties of the cell depend on a phenomenon of elective 

 solubility, certain layers of the protoplasm being impregnated 

 with a mixture of lecithin and cholesterin. All substances that 

 are soluble in this mixture, and they include by far the greater 

 number of organic compounds, being able to penetrate into the 

 living cell. The rapidity of the passage of different compounds 

 into the cell depends on their relative solubility in water and in 

 a mixture of cholesterin and lecithin. A knowledge of the 

 osmotic properties of the living protoplasm throws much light 

 on the action of many poisons and other drugs. 



Demonstration of the structure and attachment of the flagellum 

 in Euglenaviridis, by Harold Wager. The flagellum o[ Euglena 

 viridis possesses a bifurcate base, which is attached to the wall 

 of the excretory reservoir at the anterior end of the body (Journ. 

 Linn. Soc. Zool. vol. xxvii. p. 463). As it passes to the exterior 

 through the gullet, an enlargement occurs in the region of the 

 eye-sput. This structure can be seen in very favourable cases in 

 the living condition, but usually only after the action of reagents. 

 The best reagents for this purpose are either a i per cent, solu- 

 tion of osmic acid or a 2 per cent, solution of bichromate of 

 potash with a i per cent, solution of osmic acid. The structure 

 may be obscured by small grains of paramylon, which sometimes 

 accumulate at the anterior end of the body. 



The behaviour of the nucleolus during karyokinesis in the 

 root-apex of Phaseolus, by Harold Wager. From a study of 

 the changes undergone by the nucleolus during karyokinesis in 

 cells of the root-apex of Phaseolus multijlorus, the following 

 chief results have been obtained. 



(i) The nucleolus is the most conspicuous object in the 

 nucleus of the young meristematic cells. The nuclear network 

 forms a delicate peripheral layer only in the resting nucleus. 

 (2) The nucleolus stains deeply in hematoxylin, the nuclear 

 network slightly ; in safranin and gentian violet the nucleolus 

 stains red, the nuclear network light blue. (3) In the resting 

 condition of the nucleus the nucleolus is suspended to the 

 nuclear network by delicate filaments. (4) The nucleolus 

 often shows a vacuolar structure. (5) In the process of nuclear 

 division the nucleolus first of all becomes irregular in shape, 

 and the nucleolar substance appears to pass, by means of 

 the connecting strands, into the nuclear network, which 

 thereby becomes more prominent. (6) As the chromosomes 

 are formed the nucleolus disappears, but a portion of the 

 nucleolus is often visible in the equatorial plate. (7) The 

 chromatic substance of the chromosomes appears to be derived 

 almost entirely from the nucleolus. (8) As the daughter-nuclei 

 are being formed the chromatic substance of the chromosomes 

 runs together into small spheres, which ultimately fuse to form 

 the single large nucleolus. 



On double fertilisation in a dicotyledon, Caltha palustris, by 

 Ethel N. Thomas. The polar nuclei of this plant unite before 

 fertilisation, but that there is no absolutely fixed period is shown 



