ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 819 



Power of Plants to absorb Carbonic Oxide.* — L. Just has 

 subjected Azolla caroliniana and Lemna gibba to a series of experi- 

 ments for the purpose of determining whether plants can assimilate 

 CO in the place of C0 2 . He finds that this gas is not absorbed 

 by green plants ; but that it is injurious only when its proportion in 

 the atmosphere exceeds 10 per cent. It then prevents the formation 

 of chlorophyll, and hinders assimilation and growtb. If the gas is 

 then removed, the plant may partially recover. Chlorophyll-Brains 

 have no power of absorbing carbonic oxide. Control-experiments were 

 also made on the same plants under the same circumstances with pure 

 air entirely free from carbonic acid gas and with air containing the 

 normal amount of this gas. 



Formic Acid in Plants.f — In addition to the somewhat doubtful 

 occurrence of free formic acid in the stings of the stinging-nettle and 

 similar structures, A. Vogel records an undoubted instance in a powder 

 which occurs in commerce made from the hairs of Negretia pruriens. 

 The quantity, however, is very small, and the author thinks that, both 

 in this case and in that of the irritating fluid of the stinging-nettle, 

 the irritation is partly mechanical, due to the large amount of silica 

 present in the part of the hair which enters the wound. 



The presence of formic acid in the vegetable kingdom is easily 

 explained by the oxidation of albuminoids and of carbonic acid, and by 

 the action of oxalic acid on glycerine. In addition to the stinging- 

 nettle, it has been detected in the leaves, bark, and wood of the spruce 

 fir, in the sap of the house-leek (Sempervivurn tectorum), and in the fruits 

 of the tamarind, and of Sapindus Saponaria. Its well-known occur- 

 rence in honey, where it is accompanied by other vegetable acids, 

 probably lactic, malic, and oxalic acids, is due to its excretion from 

 the stinging-gland of the bee. The proportion present in new sugar 

 averages about 1 per cent. It has the effect of hindering fermentation, 

 and hence promoting the preservation of the honey. 



Function of Lime-salts.} — H. de Vries points out that there 

 is hardly any experimental evidence in support of the ordinary 

 theory of the part played in the life of the plant by calcium oxalate, 

 viz. that the oxalic acid is a product of the albuminoids, and that 

 its function is to decompose the calcium phosphate and sulphate, 

 the lime being the carrier of phosphoric and sulphuric acids to the 

 plant. On the contrary, the formation of albuminoids and of calcium 

 oxalate appears to go on quite independently of one another, while 

 protoplasm has an alkaline reaction, and cannot therefore contain 

 free phosphoric or sulphuric acid. 



The fact that the amount of lime deposited in the leaves increases 

 continually with their age appears to point to the conclusion that it 

 is an excretory product. The ordinary theory that calcium oxalate 



* Forsch. aus dem Geb. der Agriculturphysik, v. p. 60. See Naturforseher 

 xv. (1882) p. 336. 



t SB. Math.-phys. Klasse Munch. Akad., 18S2, p. 345. See Xaturforscher, 

 xv. (1882) p. 355. Cf. Pharm. Journ., xiii. (18S2) p. 269. 



J Vries, H. de, ' Ueber die Bedeutung der Kalkablagerungen in den Pflanzen 

 34 pp. (Berlin, 1881). See Bot. Centralbl., x. (1882) p. 194. 



