ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 257 



There are, however, starch-grains which contain amylodoxtrin and 

 dextrin, in addition to starch-substance ; but they are readily distinguished 

 from normal starch by being coloured red-violet or an intense red with 

 iodine. The different behaviour of the different layers of starch-grains 

 Meyer believes to depend on their different degrees of porosity, the 

 substance of all the layers being destitute of water, and alike physically 

 and chemically. 



Presence of Glyoxylic Acid in Plants.* — MM. H. Brunner and E. 

 Chuard consider glyoxylic acid to be formed by a process of reduction. 



In the first place oxalic acid is produced by the reducing action of 

 hydrogen on carbonic acid. 



2H,C03 + H2 = 2H2O + C2H2O,. 



Oxalic acid is then reduced in a similar manner to glyoxylic. 



C2HA + H, = H2O -f C^H.Os. 



Erlenmeyer considers that the hydrogen in the above equation is ob- 

 tained from water, which, under the action of light and chlorophyll, breaks 

 up into hydrogen and hydrogen peroxide. Glyoxylic acid, on reduction, 

 produces glycolic, tartaric, malic, and succinic acids. 



The authors used various materials for the extraction of glyoxylic acid 

 unripe grapes were first tried, but the quantity found was small. Better 

 results were obtained with unripe pears and apples, and with the fruits 

 and leaves of Bibes Grossularia and It. nigrum. 



Glyoxylic acid may be considered as the first member of the series 

 which contains formic, glycolic, and oxalic acids, and it is especially found 

 in very young fruits at an early stage of their development. The other 

 acids make their appearance and increase little by little as the fruit 

 developes, while the first-named members decrease in quantity or even 

 disappear at the moment of maturity. This is especially the case with 

 glyoxylic acid. 



Micro-chemistry of the Epidermal Tissue.f — M. J. Dufour describes 

 a number of substances found in the epidermal tissue of plants, the study 

 of which is specially interesting as throwing light on some of the physio- 

 logical functions of that tissue. The substances he classifies under various 

 heads. 



(1) Tannins. — Tannin is widely distributed in the epidermal tissue ; it 

 occurs more frequently in the upper epidermis than in the lower, often 

 presenting the appearance of drops of oil, but these are easily distinguished 

 by their dissolving in water. Two principal forms are met with, which 

 are distinguished by the colour given with salts of iron, one being blue 

 and the other greenish-black. Examples of the first form are Bhus glabra 

 and LytJirum tomentosum ; of the second, Bupleurum longifolium. The 

 epidermal tissue of ferns frequently contains tannin, as Aspidium LoncMtis, 

 A. Filix-mas, Cystopteris alpina, &c. 



On adding alcohol to an epidermal tissue, a colourless finely granular 

 precipitate is sometimes obtained; this, the author states, is frequently 

 due to tannin. Such a precipitate is obtained with Lychnis Viscaria, 

 ErantMs hyemalis, &c., and with Leguminosae and UmbelliferEe. 



Iodide of potassium gives generally a brown or colourless precipitate 

 with tannin ; sometimes a yellow or orange colour is obtained, e. g. Del- 

 phinium staphisagria and Daphne Laureola. 



* Bull. Soc. VauJ., xxii. (1886) pp. 162-9. t Ibid., pp. 134-42. 



