September, 1913. 



KNOWLEDGE. 



345 





cleared up it will be impossible to predict the moon's longitude 

 with the precision required for astronomical purposes. We 

 shall be obliged to correct the moon's mean longitude from 

 time to time, perhaps at intervals of ten to twenty years from 

 observation." 



THE MAGNETIC FIELD OF THE SUN.— Nature for 

 July 17th contains an interesting article on Professor Hale's 

 recent work in this direction. It will be remembered that the 

 hydrogen vortices round sunspots gave evidence by the 

 Zeeman effect (i.e., the doubling or tripling of spectral lines) 

 of the passage of the rays through a magnetic field, which it 

 was reasonable to conclude was caused by the whirling motion 

 of negative electrons. The present investigation has been a 

 search for a similar but much weaker effect due to the general 

 magnetic field of the sun. Great dispersion is required, as the 

 field is weak, and the Zeeman effect slight ; the new 164-feet 

 tower telescope and 75-feet spectrograph at Mount Wilson 

 have been used, which make one Angstrom = 4-9 millimetres ; 

 the distance between the D lines is 29 millimetres, or over an 

 inch. Full details are given in Nature of the manner of 

 taking and measuring the spectrograms. It will suffice to say 

 here that the spectrograms are divided into narrow longitudinal 

 strips, polarised in opposite directions, so that alternate 

 members of the doublets appear on alternate strips, 

 and the lines as a whole have an " in-and-out " appear- 

 ance. The shifts follow a sine-curve fairly regularly, being 

 at the equator and poles, and reaching maxima in opposite 

 directions at latitude 45° north and south. The maximum 

 displacement in either direction is about -006 millimetres. 

 It is concluded that the north magnetic pole of the sun lies at 

 or near the north pole of rotation, and that the strength of 

 field at the pole is about fifty Gausses. The lines belonging 

 to high levels of the sun's atmosphere show practically no 

 displacement, so it is concluded that the field falls off rapidly 

 as we ascend from the photosphere. It is incidentally 

 suggested that the tiny pores, which appear at all parts of the 

 sun, are incipient vortices which, under favourable conditions, 

 develop into spots. The whole investigation is a striking 

 illustration of the power of modern methods, especially in the 

 hands of such a master as Professor Hale. He contemplates 

 further researches, so as to obtain more information as to the 

 variation of the magnetic field at different altitudes. 



BOTANY. 



By Professor F. Cavers, D.Sc, F.L.S. 



INDIAN TIMBER TREES.— The Superintendent of 

 Government Printing, Calcutta, is issuing a series of 

 extremely useful notes on Indian timbers (Forest Bulletins, 

 Nos. 16 to 21, price 4d. each), which can be obtained from 

 H. S. King & Co., 65, Cornhill, London ; Oliver & Boyd, 

 Tweeddale Court, Edinburgh; E. Ponsonby, 116, Grafton 

 Street, Dublin ; or through any bookseller. The trees dealt 

 with in the six bulletins just issued are, respectively, Gmelina 

 arborea, Pterocarpus marsupium, Terminalia tomentosa, 

 Lagerstroemia lanceolata, Ougeinia dalbergoides, and 

 Anogeissus latifolia. Each bulletin gives the distribution, 

 habit, and so on, of the tree, the properties and uses of the 

 timber, minor products, if any, and much other information, and 

 includes a specimen of the wood in the form of a thin section 

 mounted in a stout cardboard frame. The preparation of 

 these bulletins, and their issue at such an extremely low 

 price, reflect the greatest credit on the enterprise of the 

 Forest Research Institute at Dehra Dun, the officers of which 

 are responsible for their compilation, and it would be a great 

 boon were our home authorities to issue a similar set of notes 

 on British-grown timbers. 



THE FAMILY HYDROPHYLLACEAE.— In the great 

 encyclopaedia of systematic botany, " Das Pflanzenreich," 

 now being issued under the editorship of Professor Engler, 

 there has just appeared a monograph of the family 

 Hydrophyllaceae, by A. Brand (Heft 59, 210 pages. Price 

 M. 10.60). Though some members of the family are 



cultivated as border plants (chiefly species of Netnophila 

 and Phacelia), the Hydrophyllaceae are not represented in 

 Europe, and though some species occur in all the other 

 continents the great majority are American, and the family is 

 practically concentrated in California and adjacent parts of 

 North America. In several respects the family is one of the 

 most interesting among the gamopetalous Dicotyledons. The 

 geographical distribution of the genera and species presents 

 some remarkable features, which can only adequately be 

 explained on the view that the distribution was formerly much 

 more extensive than at the present day ; the few species which 

 occur outside of North America — in South America, tropical 

 Asia, Africa, and so on — appear to be remnants of former wide- 

 spread genera. The systematic position and the affinities of 

 the Hydrophyllaceae are also of great interest. The family 

 is placed near the base of the Tubiflorae — the large series of 

 Gamopetalae including such families as Convolvulaceae, 

 Solanaceae, Scrophulariaceae, Labiatae, and so on. To the 

 Boraginaceae it presents various resemblances, such as the 

 roughly hairy leaves and stems, the coiled inflorescence (the 

 so-called " scorpioid cyme "), the presence in various forms of 

 scales within the mouth of the corolla-tube, and the internal 

 anatomy; as to the last point, the family agrees with 

 Boraginaceae and Polemoniaceae in having collateral bundles 

 of the normal type instead of bicollateral bundles with 

 internal phloem such as occur in the Convolvulaceae and 

 Solanaceae. Again, the family is separated somewhat 

 widely from the Polemoniaceae by the fact that the micropyle 

 of the seed is directed upwards (as in the Boraginaceae), 

 while the structure of the ovary in Hydrophyllaceae 

 differs from that of all the neighbouring families owing to the 

 characteristic large placentas, which only rarely fuse in the 

 centre so as to produce a truly two-celled ovary — in most 

 cases the placentation is parietal. Yet there is a striking 

 correspondence between Hydrophyllaceae and Polemoniaceae 

 as regards geographical distribution. During the twenty 

 years that have elapsed since the Hydrophyllaceae were dealt 

 with in Engler and Prantl's " Pflanzenfamilien," the number 

 of known species has increased from one hundred and seventy 

 to two hundred and thirty. Like all the other volumes of 

 " Das Pflanzenreich," this monograph is more than a mere 

 technical description of genera and species, the systematic 

 portion being preceded by an interesting general account of 

 the anatomy, pollination mechanisms, geographical distribution, 

 affinities, and so on. 



BIOLOGY OF SUBMERGED WATER-PLANTS.— An 

 interesting resume of various recent publications on the 

 structure, physiology, and ecology of aquatic and marsh plants 

 is given in the current number (Vol. I, No. I, June) of the 

 new Journal of Ecology. One of the papers reviewed at 

 considerable length is by W. H. Brown (Philippine Journal 

 of Science, Vol. VIII), and deals with the relation of the sub- 

 stratum to the growth of the Canadian water-weed, Elodea 

 (Anacharis) canadensis, though the results have a general 

 bearing upon the biology of submerged water-plants. Brown 

 gives tables showing the relative growth of Elodea with and 

 without the addition of carbon dioxide to the water, in tap 

 water, and in Knop's nutrient solution, with and without soil, 

 rooted in and simply anchored over soil or sand, and so on, 

 and the results from this portion of his work are summarised 

 as follows : — Sufficient carbon dioxide to keep the plant grow- 

 ing or even alive does not diffuse from the air into the water 

 during winter and spring ; the substratum probably serves as 

 an important source of this gas. The Elodea is not dependent 

 on its roots for absorption of mineral salts ; the chief function 

 of the roots (in this and doubtless in other submerged rooted 

 aquatics) is to anchor the plant to the soil, which is advan- 

 tageous when the soil contains organic matter and gives off 

 carbon dioxide ; plants rooted in good soil grow better than 

 those simply anchored over the same soil. When carbon 

 dioxide was supplied by a generator instead of by the soil, 

 rooted and anchored plants grew about equally well; with 

 similar soils but no external supply of carbon dioxide, floating 

 plants grew better than rooted ones, the air being in this case 

 the source of carbon dioxide. 



