296 



NA TURE 



[January 26, 1899 



a spoon or such-like article the light is readily produced, and 

 when two such masses are rubbed together a very strong glow is 

 the result. Thos. Sikei,. 



Colonial Sugar Kef. Co., Ltd., Sydney, N.S.W. 



The Wanton Destruction of Rare Visitants to our 

 Shores. 



In the Zoologist for this month (No. 691) is recorded the 

 destruction and capture of the following rare bird visitants to 

 our shores : — Six crossbills, one goshawk, one flamingo, one 

 little bustard, one great shearwater, one avocet, and two Scla- 

 vonian grebes. Is it not time this .senseless and unwarrantable 

 destruction of these beautiful creatures ceased ? Will you, as 

 the leading scientific journal, lift up your voice against it, and 

 earn the gratitude of every lover of nature? 



Rottingdean, Sussex. E. L. J. Ridsdale. 



EXPERIMENTS ON THE AUTUMN 

 COLOURING OF PLANTS. 



THOUC.H in the course of the present century a good 

 deal has been written as to the causes of the autumn 

 tints of leaves, our knouledjje of this subject is still in a 

 very unsatisfactory condition. The following notes may 

 serve to show the nature of some of the principal factors 

 involved. 



While engaged on some osmotic experiments in the 

 summer of 1897, I made the observation that the newly- 

 formed leavesof specimens of Hydrocharis morsus-ranae., 

 which had been placed some days previously in a weak 

 solution of cane-sugar, assumed a rich reddish-brown 

 colour, although otherwise perfectly normal. Further 

 experitnents showed that the culture of this plant in 

 solutions of cane-sugar, grape-sugar and fructose con- 

 stantly has this effect on the colouring of those leaves 

 which are developed during the sojourn of the specimens 

 in these solutions, and that even the leaves which were 

 fully developed before the commencement of the experi- 

 ments gradually become of the same reddish-brown hue. 



This colour is due to the appearance of red cell-sap in 

 the palisade-cells, and in the cells lining the air-chambers 

 of the leaf. .A. certain number of these cells often contain 

 red cell-sap under normal conditions, especially if the 

 plants are strongly insolated, and the temperature of the 

 water in which they are living is somewhat low ; but under 

 these conditions, the leaves never assume a colour ap- 

 proaching to that of plants cultivated in sugar solutions. 

 If the sugar solutions are changed often enough, the 

 plants remain perfectly healthy for weeks, and multiply 

 rapidly by means of suckers. In one set of experiments 

 I have followed the development during four successive 

 generations. 



In specimens of Hydrocharis grown in a good light the 

 leaf-stalks, suckers and roots are usually more or less 

 dotted with red under normal conditions ; but the number 

 of cells containing red cell-sap is very much increased in 

 these parts of the plant, if the specimens are cultivated in 

 a sugar solution, even though the conditions of light and 

 temperature arc much less favourable for the production 

 of the red pigment than in the specimens grown in pure 

 water. 



Salt solutions and the solutions of organic compounds 

 other than the carbohydrates have no such effect on 

 Hydrocharis, and even among the sugars galactose is 

 entirely without effect. Lactose acts only after a long 

 period, and the effect is even then very slight and is 

 probably due to hydrolysis. 



A few experiments with Lemna minor and with Pola- 

 moi^eton pofolialus in solutions of various sugars not 

 leading to similar results, I should prob.ibly have laid 

 the whole subject aside, had not my attention shortly 

 afterwards been drawn to the red-colouring of plants in 

 general by a tour in the Upper Engadine just at a time 

 when the autumnal colouring of the Alpine plants was 

 reaching its climax. . 



NO. 1526, VOL. 59] 



There, among the magnificent tints that overspread 

 the mountain slopes, my mind naturally reverted to my 

 laboratory experiments and the possibility of a correla- 

 tion between the two sets of phenomena suggested itself. 

 Observations and experiments, made upon the spot, led 

 me to the conclusion that there were good grounds for 

 the conjecture that an increase of sugar at the cost of 

 starch might be <>//<■ of the factors concerned in the form- 

 ation of the red pigment of those leaves which become 

 red in autumn. 



Of such leaves there are two distinct classes. The one 

 set comprises the perennial leaves, and those leaves which, 

 formed during the later part of the summer, remain alive 

 till the following spring or summer. This set of leaves (with 

 the exception of those which die in spring) lose their 

 reddish hues with the return of warmer weather {e.g. 

 holly, ivy). The other set comprises those leaves which 

 fall and die soon after attaining their reddish tints. 



Lidforss ' has drawn attention to the fact that during the 

 winter the leaves of our native plants are entirely devoid 

 of starch, but contain large quantities of sugar. Without 

 a previous knowledge of Lidforss' paper, I obtained the 

 same results and found that the deciduous leaves at the 

 time they assume their autumn tints contain more sugar 

 and less starch than in midsummer. 



The remarkable coincidence of the appearance of red 

 cell-sap with the increase of sugar in autumn and its 

 disappearance in spring at a time when the greater part 

 of the sugar in the leaf is recondensed to starch, together 

 with my observations on Hydrocharis, formed the starting 

 point for a considerable number of experiments on the 

 formation of the red pigment of leaves. 



These experiments and observations have led me to 

 conclusions which may be stated broadly thus :— 



The red colouring matters of green plants are probably 

 of the nature of glucosides, and are in most cases unions 

 of tannin compounds with sugar. 



The chief physical factors in their production are : (a) 

 sunshine, which on the one hand augments assimilation 

 and the production of sugar, and on the other hand 

 accelerates the chemical process leading to the formation 

 of the pigment ; and [b] a low temperature, which pre- 

 vents the conversion of the sugar into starch. In other 

 words, the red autumnal tints are in great measure the 

 direct result of the autumnal climatic conditions. 



It is possible in many plants to produce (red) autumnal 

 tints at any time of the year, by feeding them with glucose. 



Generally speaking, this artificial production of red cell- 

 sap is possible only where the natural reddening of the 

 leaf has its seat in the mesophyll cells. In cases where 

 the coloration is in the epidermis, experiments with 

 glucose are unsuccessful. 



Among plants especially favourable for experiments on 

 the artificial production of red cell-sap, I may mention 

 \arious species of Lilium {L. Martagon, L. iaiiiiidum, L. 

 iniibcllifcrum). Holly {Ilc.v aguifolium), \arious succu- 

 lent plants, such as Saxifraga crassifotiuiii, and among 

 water-plants, besides Hydrocharis, the different indi- 

 genous species of Utricularia. 



.\ full account of these experiments, together with 

 their connection with various phenomena of plant-life, 

 will appear shortly in ihtt Ja/irhiiclier fiir 'u'isscnschafttickc 

 Botanik. E. Overton. 



THE GREAT CATALOGUE OF BIRDS. 



THE recent issue of the twenty-sixth volume of the 

 "Catalogue of Birds in the British Museum '"- (the 

 twenty-seventh and concluding volume having been 

 published in advance in 1S95) brings to an end a 



I Botan. CcHtraWlatl. llil. 68. p. 33 44 (1896). 



- " C.il.-iloguc of ttic PlatBlcffi. Herodioiies. Sw^anopodcs, Pygonodes, 

 Afc-c, and Impennes in llic Colleclion of the Brinsh Museum." By R. 

 Howdler Sliarpc and W. R. Ogilvic-Grant. (London, 1898.) 



