KNOWLI.DGi:. 



January. 1912. 



are only rough, but may st-rve lo indicate the principal details 

 shiiwn on the plates. .X recent journal of the Astronomical 

 Society of Canad.i contains .1 reproduction of a beautiful 

 photograph of Mars taken by I'rofessor Barnard at Verkcs in 

 I'lO'i, Those taken in that year with the ►.'real relleclor at 

 Mt. Wilson were very successful in showiut; the various 

 shadiuKs on the Maria, but broke down in fuie detail : a 

 refractor has the ,'idvanl:iL;(' in this respect. We have reached 

 a sta^e when photO(;raphy lUH^^^ii" '" ^"■' '' '*-'■*' <t><J ■■■ "'■<' 

 study of the planet. *<• 



1;NCKK'S COMirr.— The re.ison of the large discord- 

 ance between prediction and observation in the positions 

 of l-"nckc"s comet last suintner has been detected. Through 

 an nnfortun.ite erratum the epheineris was coniputed from 

 elements in which the eccentric angle was lo' too small. A 

 corrected ephemeris has now been forined. and I'rofessor 

 Hackhmd gives in Astr. Xnchrichtvn. No. 45J9, a comparison 

 with the observations. The values of observed minus computed 

 (piantities are as follows : 



Dale, Observed Computed. No. of 



I'lace. 1911. R.A. Dec. Nights. 



Algiers July 31 ... -l"-58 ... + 8"-3 ... 1 



Cape Sept. 6 ... +0"-14 ... + 4"- 6 ... H 



Johaimesburg ... Sept. 9 ... +0"-03 ... - 4"-.S ... 11 

 S.intiago,Chili ... Sept. 24 ... +r-41 ... -26"-3 ... 1 

 It is clear from these figures that the predicted date of 

 perihelion is very nearly right, and Dr. Backlund concludes 

 that his value of the mass of Mercury 1 9,700,000 is confirmed, 

 and that the acceleration of the mean motion of the comet 

 suffered a notable diminution about the time of perihelion in 

 1904. 



SCHAU MASSES COMICT.— The eighth cometary dis- 

 covery of 1911 was made on November 30th, by M. 

 Schaumasse, an a.ssistant at the Nice Observatory. It was 

 only of the twelfth magnitude but will probably be of at 

 least the tenth in January. The elements are : — 

 T = 1912, Feb. 5-35, G.M.T. 



w = 109° 8' 



a = 115° 12' 



i = 20° 29' 



q = 1-170 

 Position on January 1st, R A 15'' 17"* 52^ S. Dec. 1° 47', d.iily 

 motion + 4.5'"'", South 15'. It is a morning star, rising some 

 5^ before the Sun. 



BOTANY. 



By Proi-essor F. Cavers, D.Sc. F.L.S. 



STKCCTURE OF CLOSTERIUM. — Two interesting 

 papers have recently been published on the structure of this 

 beautiful genus of Desmids. by Lutman {Bot. Oaz., April, 

 1910 and June, 1911). Clostcriiiin is a large genus (with 

 about si.xty British species, for instance), and is easily 

 recognised by its elongated cell, which is usually curved and 

 t)ften markedly semilunar in form, tapering at each end to a 

 pointed tip or pole. At each pole, there is a vacuole con- 

 taining minute particles of calcium sulphate, suspended in 

 liipiid and showing vibratory movement; Clostcriiiin is also 

 interesting as showing active streaming movements of the 

 protoplasmic layer within the cell-wall. 



In his lirst paper, Lutm.in shows that the descriptions 

 hitherto given of the structure of the chromatophore or 

 chloroplast are inaccurate. His methods of sectioning the 

 plants with the microtome show that each of the two chrom- 

 atophores consists of a hollow cone bearing relatively 

 narrow longitudinal ridges on its outer surface— the number 

 of these ridges is greater than has been previously described, 

 and they may be as many as eighteen and rarely fewer than 

 twelve. App.irently it is practically impossible to count the 

 number of the ridges accurately except in sections. All 

 previous writers on this Desmid have descrilied the chromato- 

 phore as consisting of a solid longitudinal axile rod bearing 

 a number of radiating plates. Lutman shows, however, that 

 this is not the case and that in cross section the chromato- 



phore does not resemble a hub with radiating spokes, but is 

 more like a coarsely-cogged wheel. The protoplasm in the 

 furrows betwei-n the ridges of the chromatophore is fretpicntly 

 nuieh denser in structure than the chromatophore itself, but 

 contains mmierous vacuoles of varying sizes ; however, there 

 are great differences in this respect, and sometimes this pro- 

 toplasm is reduced to a mere network occupied almost 

 entirely by vacuoles. The external appearance of the plant 

 is determined largely by the density of the protoplasm 

 between the ridges ; sometimes the plants are so dark green 

 as to be almost opaque, at other times much lighter green and 

 semi-transparent. 



Lutman then describes the pyretioids in the two .species of 

 Clostcriiiin studied by him; in C. clircnhernii they are 

 (Mubedded in the outer portion of the chromatophore, while 

 in C. iiionilifcritin they are situated exactly at its centre and 

 are arranged in a single row along the central axis of the cell. 

 In addition to the layer of starch which encloses each 

 pyrenoid there are numerous starch grains lying free in the 

 protoplasm, usually in longitudinal rows along the ridges of 

 the chromatophore. The free starch grains exactly resemble 

 the pyrenoid ones, being angular at the edges and concave 

 and clearly originated around a pyrenoid. It is difficult to 

 say whether these free starch grains became free by a second 

 layer of starch being formed around the pyrenoid and 

 crowding out the old layer, or by the breaking-up of the 

 pyrcnoids them.selves. In size the pyrenoids vary from 

 bodies almost impossible to see with the highest magnification 

 to spheres whose diameter is one-fifteenth that of the 

 Clostcriiiin body itself. The starch is present as a layer of 

 irregularly-shaped grains, but sometimes more than one layer 

 is suggested by the appearance of other grains just outside the 

 regular layer. No two pyrenoids are alike as to the shape of 

 the grains around them ; there is no stratification visible in 

 either grains or pyrenoids. Where strands of protoplasm run 

 across the central part of the cell body, they tend to be 

 oriented on the pyrenoids, exactly as in Spirogyra, and so 

 on; this arrangement, which is doubtless connected with the 

 streaming movements of the protoplasm, puts the pyrenoid in 

 <|uick communication with all parts of the cell, and facilitates 

 the movement of food materials toward and aw.ay from it. 

 The pyrenoids may be angular or rounded : they often contain 

 denser and lighter portions, and sometimes a vacuole: they 

 often divide up into a number of discs or segments of varying 

 niuuber and form. If plants are kept in darkness for a few 

 days, the starch around the pyrenoids rapidly disappears, 

 while the pyrenoids themselves are found to have diminished 

 one-third to one-fourth in size — showing that some of the 

 pyrenoid substance has been used up. 



In his .second paper, Lutman deals with the structure and 

 division of the nucleus in Clostcriiiin. The nucleus lies at 

 the central and thickest part of the cell, between the two 

 chromatophores. and has the form of a double convex lens. 

 It consists of a fine network of lightly-staining fibres, with a 

 mass of deeply-staining granules in the centre. The first 

 external sign of division is a pinching-in of each of the two 

 chromatophores, at about a third of the distance from middle 

 to tip of the cell, as if it were being constricted by a rubber 

 band around it at each of these two places. The chromato- 

 phore, in fact, seems to divide in the way the entire cell 

 divides in animals like Amoeba. Meanwhile, the nucleus pro- 

 ceeds to divide, and after the chromosomes have been drawn 

 to the two poles, and across the middle of the cell, there now 

 appears a broad granular b.iiid in which the new cell-wall is 

 formed. The two new nuclei then pass alotig, within the cell- 

 wall, lo the new position they are to occupy permanently in 

 the new cell at the middle of each chromataphore. Soon after 

 the new cross-wall is put in at the middle of the Desmid. the 

 new end begins to round out, but the two individuals hang 

 together for (piite .1 time with only a slight comuction, which 

 finally breaks, the individu.ils separating before the new h.alves 

 are at all symmetrical with the old ones. 



Lutman deals with the apparently unequal division of the 

 chromatophore. A Clostcriiiin plant is, apart from its 

 curv.ature, composed of two cones placed base to base, and 

 when the chromatophore in each half divides, by a plane 



