R2 



KNOWLEDGE. 



TApeil 1, 1901. 



spines ; but when the bush grows into a tree, and bears 

 leaves far above the reach of browsing animals, the un- 

 necessary spines disappear, and the edges of the leaves 

 are entire. In the Blackthorn and Hawthorn, the strong 

 spines are modified branches ; and we may observe that 

 they are much more numerous in young plants than in 

 old biishes. A more complicated mode of protection is 

 foimd in the Nettles. They are furnished with hollow 

 hairs, filled with a virulent fluid, and bent at the tip. 

 A slight pressure causes the curved extremity to break 

 across, leaving a slender tube, tapering to an extremely 

 fine point, which easily enters the flesh and discharges 

 a portion of its venemous contents. 



So far we have considered leaves as fidfiUing their 

 normal functions of producing plant food by means of 

 chlorophvll cells. In conclusion, brief reference may be 

 made to various exceptions; for the production of plant- 

 food is not necessarily carried on by leaves, nor is the 

 use of leaves altogether limited to the production of 

 plant food. First, leaves may be dispensed with, as we 

 have already seen in the case of the Gorse. The stem 

 may be modified to supply the place of leaves, as in the 

 Butcher's Broom, whose flattened " leaves " are really 

 branches, as we see when we find flowers and fruit borne 

 on these flat leaf-like structures. In climbing plants the 

 leaves, or a portion of them, are frequently converted into 

 tendrils, often endowed with a marvellous sense of touch, 

 for gi-asping supports and thus aiding the plant in its 

 upward climb through surrounding herbage to the light. 

 This is seen in many of the Vetches, the upper end of 

 whose leaves are modified in this fashion. In the Yellow 

 Vetchling (Lnfhyrus aphaca) a further modification has 

 taken place. The whole leaf is converted into a tendril, 

 while the stipules (the. usually small pair of leaf-like 

 appendages that often grow at the point where a leaf 

 joins a stem) are enlarged into a very respectable pair of 

 " leaves." and manufacture food while the tnie leaf 

 helps the plant to climb. Of other much stranger modi- 

 fications of leaves Mr. Pearson has written in Know- 

 ledge last year. Vol. XXIII., pp. 245-6— of the mar- 

 vellous tentacles which the leaves of the Sundew bear, 

 which catch and digest insects; and how certain leaves 

 of the Bladderwort are converted into snares on the most 

 approved rat-trap plan, for the same purpose — some of 

 the most mar\'ellous fairy-tales of botany. 



Astronomical. — The recent observations of Eros have 

 resulted in the remarkable discovery that the planet is 

 probablv accompanied by a satellite nearly as large as 

 itself. The first mdication of this fact was the detection, 

 by Dr. Oppolzer, of variability to the extent of about a 

 magnitude in the luminosity of the planet in the period of 

 a few hours. Confirmation ■ of the variability has been 

 obtained by two French astronomers. M. F. Rossard 

 found the magnitude to range between 9-3 and 11 on 

 February 14th, loth, and 16th, and concluded that the 

 period was 2h. 22m. M. Ch. Andre believes that his 

 observations indicate a period of about six hours, and 

 states that the light-changes are similar in character to 



those of the well-known variable TJ Pegasi ; the system 

 being probably composed of two asteroids, with diameters 

 in the proportion of three to two, the plane of revolution 

 passing through the earth. As the inclination of the 

 plane of revolution to the line joining Eros and the earth 

 changes, corresponding differences in the variability may 

 be expected. 



There is every indication that adequate records of the 

 total eclipse of the sun on ilay 18th will be obtained, if 

 the weather should fortunately be favourable. Mr. and 

 Mrs. Maunder will be stationed in Mauritius, where they 

 wiU work in conjunction with Mr. Claston, the Director 

 of the Royal Alfred Oliservatory, In Sumatra, where the 

 duration of totality on the centi'al line is over six minutes, 

 there will lie quite an army of astronomers, including 

 Mr. Dyson, of Greenwich; Mr. Newall, of Cambridge; 

 parties from the Lick, Yerkes, and Washington Observa- 

 tories, and a Dutch expedition under the direction of Dr. 

 Nijland. Photographs of the corona on a large scale, to 

 show the details near the sun's limb, and on a smaller scale 

 to depict the streamers, will be attempted, in addition to 

 spectrum photographs with sUt spectroscopes and prismatic 

 cameras. 



An extensive comparison of sun-spot and magnetic 

 data which has been made by Father Sidgreaves, 

 supports the view that the distinct connection disclosed 

 cannot be due to a direct action of the sun upon the 

 earth, but rather that there is a common cause for 

 both. Large sun-spots are frequently unaccompanied 

 by magnetic storms, and the cause therefore does not 

 always affect both the sun and the earth at the same 

 time. 



The discovery of sixty-four new variable stars is 

 announced in Harvard College Observatory Circular 

 No. 54, a large proportion of them having been found 

 from the presence of bright hydrogen lines in their spectra. 

 Many stars whose spectra are of the fourth type also 

 prove to be variable. These varialdes have been divided 

 into two classes. First, those in which the variation is so 

 great that it is obvious to the most inexperienced obsers"er. 

 Secondly, those in which the variation so far detected is 

 small, about half a magnitude to a magnitude. In each 

 of these cases, two or more experienced observers, who 

 are accustomed to accurate measures of photographic 

 brightness, are satisfied that the change is real. — A, F. 



Botanical, — Under the heading "' Economy in Nature," 

 in Turreya, a new publication of the Torrey Botanical 

 Club, Mr, P, A. R\db?rg mentions a cherry tree which, 

 till quite recently, giew in New Orange, New Jei-sey, 

 It had an unusually thick trunk, which divided at about 

 seven feet from the ground into two trunks. At the 

 junction of these was a large hole, showing that the 

 stem was decayed and hollow, A strong wind tore 

 away one of the trunks, when it was found that the 

 hoUow stem was partly filled with refuse, consisting of 

 decayed cherries and leaves. Into this a stout root, 

 originating from the margin of the hole, had gi-own, 

 and had then sent off numerous branches into the 

 decaving stem of the tree, which was thus actually 

 preying upon itself, 



BracJi t/ifel ma Biiigeri, a new Asclepiad with an edible 

 tuber, is described and figured by M. A. Chevalier in the 

 Revue des Cultures Colotuahs for February 5th, It is 

 a native of the region of the Upper Niger. The tuber 

 resembles in taste the Jerusalem artichoke, and though 

 only slightly nutritive, its value as a food is augmented 

 owing to the fact that it can be procured when supplies 

 of rice and millet are exhatisted. Other species of 



