68 SUMMARY or CURRENT RESEARCHES RELATING TO 
mode of increase in thickness, and the formation of annual rings in 
dicotyledonous trees. 
Influence of an Excessive Proportion of Carbonic Acid on the 
Growth of Roots.* — M. S. Jentys finds, from a series of experiments 
carried on chiefly on wheat and rye, that a condensation of carbon 
dioxide in the soil, even to the extent of from 4 to 12 per cent., has not 
such an injurious effect on the growth of roots as the experiments of 
Bohm seemed to indicate. The results, however, varied somewhat with 
different plants. 
Assimilation of Carbon dioxide.j* — By treating specimens of Spiro- 
gyra from which the starch had been entirely removed with substances 
which readily break up into simpler constituents, of which formic 
aldehyde is one, Herr T. Bokorny showed that these plants have the 
power of separating formic aldehyde from the nutrient solution, and 
then converting it into starch. This appears to furnish an argument in 
favour of the view that formic aldehyde is the substance first formed 
in the production of carbo-hydrates from the carbon dioxide of the 
atmosphere. 
Mode of Absorption of free Nitrogen by the Leguminosae +— 
Herr P. Kossowitsch describes in detail a series of experiments under- 
taken for the purpose of determining through what organs it is that the 
Leguminosae have the power of absorbing free nitrogen from the atmo- 
sphere. The plant experimented on was Pisum sativum , and the modus 
operandi consisted in the substitution of hydrogen for nitrogen in the 
surrounding air. The result arrived at was that in all probability, the 
root is the organ where the free nitrogen passes into the combined 
condition. 
Sigg. V. Alpe and A. Menozzi § confirm Frank’s observations of 
the absorption of free nitrogen by plants, with the assistance of microbes, 
especially by the root-tubercles of Leguminosae. 
Exchange of Gases in the Root-tubercles of Leguminosae. || — Herr 
B. Frank describes the root-tubercles of the Leguminosae ( Vida Faba ) 
as being enclosed in several layers of suberized cells permeated by inter- 
cellular passages, which penetrate the cortical tissue of the tubercle (but 
not the meristematic tissue which completely surrounds the “ bacteroid- 
tissue ”) as a perfectly closed envelope. The “ bacteroid-tissue ” is again 
itself permeated in all directions by intercellular spaces which are not in 
communication with those of the cortical layer, while these latter are so 
with the external air. The air in the “ bacteroid tissue ” must be derived 
from its own cells. When the tubercles are isolated they give off abun- 
dance of nitrogen gas after a time, especially the “ albuminoid- 
tubercles ” ; but this appears to be the result of the commencement 
of decay, and not to be a normal phenomenon. The mode in which 
* Anzeig. Akad. Wiss. Krakau, 1892, pp. 306-10. See Bot. Centralbl., lii. (1892) 
p. 93. f Biol. CentralbL, xii. (1892) pp. 481-4. 
x Bot. Ztg., 1. (1892) pp. 697-702, 713-23, 729-38, 745-56, 771-4 (1 pi. and 
6 figs.). 
$ Bull. Notiz. Agrar. del Ministero d’ Agricoltura, 1892, 32 pp. See Bot. 
Centralbl., li. (1892) p. 337. 
U Ber. Deutsch. But. Gesell., x. (1892) pp. 271-81. ^ Cf. supra, p. 63. 
