86 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
position of stable equilibrium in hydrostatic suspension. In its natural 
direction the root always curves at a definite point, which presents a 
coefficient of minimum flexion, and the position of which depends on the 
order of the root. The orientation of the extremity of a root in hydro- 
static suspension depends on the form of the extremity. The laws of 
gravity are sufficient to cause roots to grow in a vertical direction, and 
to bring them back to this direction when they have departed from it. 
Assimilation of Free Nitrogen by Plants. — Herr B, Frank * * * § sums 
up the results obtained by the researches hitherto made on this subject, 
and reiterates his own previous conclusions, viz. that (1) The Legu- 
minosa© assimilate free nitrogen, even when not in symbiosis with the 
tubercle-fungus. (2) The symbiotic fungus of Leguminosa©, when culti- 
vated apart from its host-plant, developes vigorously when it can avail 
itself of an organic compound of nitrogen, but only feebly when nitrogen 
is presented to it in the elementary form. (3) The quantity of com- 
bined nitrogen which accumulates in the root-tubercles is not nearly 
sufficient to supply the amount which mature Leguminosae, even when 
grown in soil destitute of nitrogen, possess in their seeds and other 
organs. (4) Plants not belonging to the Leguminosse also assimilate 
free nitrogen, viz. fungi, certain alga© and mosses (especially species of 
Oscillatoria, Nostoc, Ulothrixy, and certain flowering plants (Arena saliva , 
Polygonum Fagopyrum , Spergula arvensis, Brassica Napus , Sinapis alba, 
Solanum tuberosum, Acer platanoides). (6) The value of nitrates as 
manures is greatest when the plant is young and its power of assimi- 
lating free nitrogen is still very small. 
On the other hand, Herr A. Petermann f states that fresh experiments 
have led him to doubt the correctness of his previous results, as far as 
barley is concerned, and rather confirm those of Hellriegel, Wilfarth, 
Schlcesing, and Laurent, that the power of fixing free nitrogen belongs 
to the Leguminosse alone, and is not possessed by plants belonging to 
other natural orders. 
MM. T. Schloesing and E. Laurent { also give further experimental 
evidence that flowering plants not belonging to the Leguminosse have 
no power of fixing free nitrogen. This property is, however, possessed 
by some algae of low organization which occur commonly on the surface 
of the soil, such as Nostoc, PJiormidium , Cylindrospermum, &c. It may, 
in these cases, be due to a symbiotic connection of the algae with 
bacteria. 
Experiments by Mr. C. X). Woods § on several leguminous plants 
confirm previous results. 
Prove [| suggests that the predisposition to form root-tubercles is 
transmitted to certain individuals by heredity, while it is absent from 
others. 
* Bot, Ztg., li. (1893) l‘e Abtheil., pp. 139-56. 
t Bull. Acad. R. Belg., xxv. (1893) pp. 267-76. Of, this Journal, 1893, p. 357. 
% Ann. Inst. Pasteur, vi. (1892), pp. 824-40. See Journ. Chem. Soc., 1893, Abstr., 
p. 336. 
§ Rep. Storrs School Agric. Exp. Stat., 1892, p. 17. See Bot. Centralbl., 1893, 
Beih., p. 303. 
|| Zeitschr. Landwirthsch. Ver. Bayern, lxxxii. (1892) pp. 85-100 (2 figs.). See 
£oi. Centralbl., Iv. (1893) p. 185. 
