2(2 



NATURE 



\yuly 12, 1877 



dioxide as in common air, and well developed green 

 gourd leaves, were tried. The gourd leaves, which con- 

 tained starch at the beginning, entirely lost it within a day 

 or two in the atmosphere deprived of carbon dioxide, 

 while those in the oiher shade remained still full of it. 

 The shades, and the contents of the dishes, were then 

 changed, so as to bring the starchless leaves into the 

 shade containing carbon-dioxide. During the day these 

 became again lull of starch ; while within twenty-four 

 hours it had quite disippeared from the leaves in the 

 other shade. In a similar experiment with sugar-beet the 

 control plant in the open air was covered with a black 

 paste-board box, and it was found that the leaves in the 

 shade deprived of carbon-dioxide lost their starch at 

 about the same rate as those in the dark. In no case was 

 starch found in the leaves while they remained in an 

 atmosphere without carbon-dioxide. 



The second set of experiments was made with long 

 leaves of bulrush and bur-reeds, which were etiolated, and 

 then separated from the plants. With the same general 

 precautions as before,the upper end of the leaf was inserted 

 in the shade without carbon-dioxide, the lower in an 

 atmosphere containing five per cent, of carbon dioxide, 

 whilst the space between was left free to the open air. 

 This intermediate part was obscured by tin-foil, so that 

 no starch could be formed in it at the expense of any 

 carbon-dioxide passing through the tissues from the 

 lower shade ; and it was supposed that if such a pheno- 

 menon were possible, the spacious longitudinal air channels 

 of these plants might be especially favourable to the trans- 

 mission of the gas. These expeiiments usually lasted 

 one day, and uniformly gave the same result ; starch was 

 formed abundantly where carbon-dioxide was at disposal 

 in the air, while the excess of it in the lower shade had 

 no effect upon the portion of leaf in the upper shade, 

 which remained entirely fr-^e from starch. 

 _ The apparatus whep arranged was always placed in a 

 light window, shaded by gauze blinds if the sun were too 

 hot ; and in these latter experiments it was an interesting 

 circumstance that, in the lower portions of these rather 

 thick leaves, more starch was formed on the side next 

 to the window ; therefore, in two cases a piece of 

 looking-glass was placed behind the shade, when, being 

 equally illuminated, starch v.;as formed in equal abun- 

 dance on both sides of the leaf. This variation in the 

 starch-formation, according to the amount of light, 

 showed that that portion of leaf had not always used all 

 the carbon-dioxide at its disposal, and that consequently 

 there was an excess which might have passed upwards 

 through the tissues. 



The third set varied from these in' having no part of 

 the leaf exposed to free air, thus obviating the possibility 

 of the carbon-dioxide being diffused into it in passing 

 upwards through the plant. A glass vessel containing 

 air without carbon-dioxide was placed within a large 

 shade containing air with 5 per cent, of this gas ; and a 

 previously etiolated leaf, with its stem in water, was so 

 fixed as to be partly in the one and partly in the other. 

 After six or eight hours it was examined for starch. 

 Without exception starch was formed abundantly in the 

 parts in the large shade, whilst no trace of it was found 

 in those in the inner vessel even quite close to the junc- 

 tion between the two. 



The remaining two sets of experiments were made to 

 ascertain whether starch formation in leaves, in the open 

 air, is accelerated by giving an excess of carbon-dioxide, 

 either to adjoining parts of the leaves themselves, or 

 to the roots. In the first case leaves separated from the 

 plant were divided lengthways. One half, with the stalk 

 in water, was in a shade with air containing 5 per cent, 

 of carbon-dioxide, its upper part projecting under the 

 glass lid of the shade, which was luted with grease, into 

 the open air. The other hall of the same leaf was laid 

 on the lid, on filter paper soaked with boiled water to 



keep it moist, and put as near as possible to the pro- 

 jecting piece of leaf. In the other cases etiolated leaves, 

 organically united with plants whose roots were in rich 

 humus soil, were divided lengthways ; one half, quite cut 

 off, was laid near to the other, and the two were examined 

 and compared after some hours' exposure in sunlight. 

 The results of both these sets of experiments were uni- 

 formly the same ; careful examination showed that starch 

 was formed as readily and plentifully in those portions of 

 leaves excluded from any other source of carbon-dioxide 

 than that in the air surrounding them, as in those having 

 an excess of it at command. 



From these experiments Dr. Moll concludes that starch 

 is never formed in leaves in an atmosphere deprived of 

 carbon-dioxide, however mixh of it may be at the disposa 

 of the other, under- or above-ground, parts of the plant ; 

 nor can starch-formation be accelerated in one part of a 

 leaf by an excess of carbon-dioxide being at the disposal 

 of another part of it, either in the air, or through the 

 roots. 



The results of these elaborate experiments are doubtless 

 in accordance with the direction of those of other modern 

 inquirers on this subject. At the same time it will probably 

 be felt, that, when long-accepted opinions, which many 

 well-known facts seem to favour, are held to be called in 

 question, we may still ask for further confirmation, before 

 accepting as decisive, conclusions depending on the exact 

 interpretation of experiments made with living organisms 

 exposed to somewhat artificial conditions. It may be 

 hoped, however, that this further instalment of evidence 

 in a given sense will incite to further research. 



OUR ASTRONOMICAL COLUMN 

 De Vico's Comet of Short Period. — It has been 

 already remarked in this column that, according to Prof. 

 Briinnow's last investigations relative to this comet, it 

 appears necessary to admit a very material degree of 

 uncertainty in the value of the mean motion determined 

 from the observations of the year 1844, notwithstanding 

 the comet was discovfered on August 22, and followed till 

 December 31, or for a period of more than four months, 

 and, moreover, was observed with a degree of precision 

 which has seldom been attained with these bodies. In 

 Prof. Briinnow's masterly and elaborate discussion, 

 " M^moire sur la Comfete elliptique de De Vico," which 

 gained the prize offered by the Royal Institute of the 

 Netherlands, in June, 1848, the planetary perturbations 

 were calculated to the epoch of next return to perihelion 

 in February, 1850, but in consequence of the computed 

 positions showing that observation in that year would 

 be quite hopeless, the calculation was continued with all 

 possible precision to the ensuing perihelion passage early 

 in August, 1855. The computed track in the heavens for 

 this appearance was by no means an unfavourable one 

 for observation ; the comet would remain for a consider- 

 able period near the earth, being at its least distance on 

 August 2, just before the perihelion passage, when it 

 should have approached our globe, according to Prof. 

 Briinnow's calculation, within o'58 of the earth's mean 

 distance from the sun. Nevertheless, it was not detected 

 in this year — an object observed by M. Goldschmidt, 

 not far from its track, in May, being certainly a dis- 

 tinct body, if the star of comparison was correctly 

 identified. It was looked for repeatedly with the large 

 refractors at Cambridge and Berlin. In 1S60 again, 

 ephemerides were prepared and a search was made, at 

 least at the observatory of Harvard College, U.S., but 

 ineffectually, indeed the chance of observing this comet 

 when the perihelion passage falls in the winter must be 

 but small. 



The later results obtained by Prof. Briinnow, to which 

 allusion is made above, will be found in No. 3 of his Ann 

 Piihox Astronomical No/ices: he there gives his reasons 



