448 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
carbon dioxide greater than the volume of oxygen absorbed in the same 
time; in other words, the respiratory quotient is higher than unity. 
This respiratory quotient has a different origin, and pursues a different 
course, according to the degree of ripeness of the fruit, and its chemical 
constitution. Two kinds of respiratory quotient higher than unity may 
be distinguished, one due to the presence of acids, the other to fermen- 
tation. The acid quotient occurs whenever fruits which contain an acid 
— citric, malic, tartaric, &c. — are exposed to a high temperature; for 
fruits containing citric or tartaric acid, about 30° Q. ; for those containing 
malic acid, about 15°. The fermenting quotient is jDroduced whenever 
the oxygen of the air does not reach the cells in sufficient quantity to 
furnish the energy necessary for vital activity. This deficiency of 
oxygen is due to the production of pectin. The fermenting quotient 
differs from that of acids in the period at which it appears; in the 
lower temperature at which it is manifested ; in its higher value (often 
above 3) ; and in the corresponding intensity of respiration. 
Among the chemical changes which take place in the ripening of 
fleshy fruits are the following : — The acids are partially used up in the 
production of carbohydrates. The tannin disappears by complete oxida- 
tion without forming carbohydrates ; the starch is transformed into 
sugars, which are partially oxidised. 
Formation of Wood from Reserve-Material.* — Herr A. Wieler 
attributes the nourishment of the cambium in woody plants to three 
factors, — the supply of water, of mineral substances, and of organic sub- 
stances. Treating especially of the third of these sources, as the result 
of observations on a number of different trees, he comes to the conclusion 
that the spring-wood is essentially a product of the reserve-substances 
in the stem, the breadth of the zone being proportional to the amount 
of these substances stored up. 
Formation of Cane-Sugar out of Dextrose.* — From observations 
made on a material composed of a very large number (2000) of embryos 
of barley, Herr J. Griiss asserts that, in the process of germination, 
cane-sugar is formed in the cell out of dextrose ; cellulose and starch 
out of cane-sugar. In the formation of starch and cellulose, no substance 
belonging to the group of aldehyds is set free in the molecules of sugar. 
Yeast and Alcoholic Fermentation.^ — After a historical survey of 
the different views which have -prevailed regarding the nature of fer- 
mentation, Prof. J. R. Green thus concludes an admirable and succinct 
article. The great advances made in the study of fermentation under 
the action of soluble enzymes has drawn attention to the possibility of 
the secretion of an alcohol-producing enzyme by the yeast-cell. The 
idea of an enzyme does not necessarily involve a new view as to the 
nature of fermentation ; the secreted enzyme is merely substituted for 
the protoplasm of the cell as the active agent in the process. This idea 
is not new, having been advanced by Berthelot, Moritz Traube, and 
Hoppe-Seyler. 
The enzyme has been prepared by Buchner, § and this discovery 
* Tharander forstl. Jahrb., xlvii. 76 pp. and 4 pis. See Bot. Ztg., lvi. 2 te Abtli., 
p. 39. t Ber. Deutsch. Bot. Gesell., xvi. (1898) pp. 17-20. 
X Nature, lvii. (1898) pp. 591-4. 
§ Cf. this Journal, 1897, pp. 222 and 4 14. 
