51 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
none at all. No evidence could be obtained of tlieir increasing the 
richness of the soil in nitrogen. 
Fixation of Atmospheric Nitrogen by Algse and Bacteria.* * * § — 
M. R. Bouilhac has experimented on the power of the three algas Schizo- 
ihrix lardacea , Ulothrix flaccida, and Nostoc punctiforme to absorb free 
nitrogen from the atmosphere in pure cultures in the presence of the bac- 
teria of the soil. With the first two species the results were negative ; 
but the cultivation of the Nostoc in association with the bacteria resulted 
in a vigorous development of both species and the fixation of atmospheric 
nitrogen. The power of this alga to absorb nitrogen may be compared 
to that of the Lcguminosse. 
Influence of Light and Temperature on Turgor.f — According to 
experiments made by Mr. E. P. Copeland — on mosses and on seedlings 
of Vida Faba — the turgor is affected by temperature in a variety of 
different ways, both direct and indirect. Turgor is regulated by rapidity 
of growth, rather than the converse. With regard to the connection 
between etiolation and turgor, the turgor of the root is influenced by 
the amount of light which the aerial parts receive. Turgor is not 
affected by the removal of carbon dioxide from the atmosphere ; it is as 
high in etiolated as in illuminated parts of the plant. 
Absorption and Emission of Water by Seeds.J — As the result of 
experiments made on a number of different seeds by M. H. Coupin, it 
appears that the absorbing power for water of the same species varies 
greatly, as also does the extent to which the water penetrates the seed. 
In some saturated seeds there is water which does not belong either to 
the testa or to the embryo. Dormant seeds absorb, as a rule, as much 
water as living seeds. The absorbing power of seeds is only slightly 
influenced by the temperature. Aqueous vapour can be absorbed directly 
by seeds, especially by the embryo. 
The bursting of the testa of seeds cannot be attributed entirely 
either to the increase in size of the embryo or to the direct force of the 
germinating radicle ; it is probably due to a diastase, which decreases 
the resistance of the testa by disorganising it. 
When seeds are plunged in water dilatation takes place, followed by 
contraction, if the seed has a thin folded testa ; but contraction only if 
the seed adheres to the embryo. The contraction is due to a chemical 
combination of the reserve-materials with water; dilatation to rapid 
imbibition by the testa. When ripening, seeds become desiccated by 
transpiration, not simply by evaporation. 
(3) Irritability. 
Rheotropism.§ — Mr. F. Newcombe has experimented on the existence 
of rheotropism in Phanerogams. The experiments were made on the 
roots of suspended seedlings dipping in water. Out of 17 species of 
Monocotyledons and Dicotyledons, 8 were found to be positively rheo- 
tropic, i.e. they bent the tips of their roots directly or obliquely against 
* Comptes Rend us, cxxiii. (1896) pp. 828-30. 
t ‘ Ueb. d. Einfluss v. Licht u. Temperatur a. d. Turgor,’ Halle, 1896, 59 pp. 
See Bot. Centralbl., lxviii. (1896) p. 177. 
t Ann. Sci. Nat. (Bot.), ii. (1896) pp. 129-222 (31 figs.). 
§ Bot. Gazette, xxii. (1896) pp. 212-3. 
