ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
479 
investigations and ideas on tlie fixation of nitrogen by plants. He does 
not regard as conclusive Frank’s evidence in favour of the theory that 
this is a general property of all green plants, believing that no positive 
conclusion can be drawn from the result of experiments on plants growing 
in the open air. He calls attention to the enormous practical importance 
of the subject to agriculture. 
Fixation of Free Nitrogen by the Leguminosse.* * * § — Pursuing their 
investigations on this subject, Herren F. Nobbe and L. Hiltner confirm 
their previous statement that the assimilation of nitrogen by the plant 
is connected with the conversion of the bacteria into bacteroids ; and 
they compare the processes in the nodules to those in insectivorous plants. 
Unchanged bacteria appear to be unable to fix the free nitrogen of the 
atmosphere, the absorption commencing only with the production of 
bacteroids. The bacteroids are formed by the division, without separa- 
tion, of bacteria. In the first stage the rod divides in the middle ; the 
two poles are coloured like the unchanged bacteria, the intermediate 
space remaining colourless ; branches may ultimately be formed. Many 
leguminous plants, especially Robinia , yield a larger final gain of 
nitrogen when grown in a soil free from nitrogen than in one supplied 
with combined nitrogen, owing to the very large nodules produced. 
(3) Irritability. 
Irritability in Plants-t — The explanation offered by Errera J of the 
bending of liyphae of Phy corny ces towards iron — that it is a case of positive 
hydrotropism — is criticized by Herr F. Elfving, who dissents from this 
conclusion on the ground that other bodies which eagerly absorb water, 
such as caustic potash and calcium sulphate, do not attract the hyphse of 
Phycomyces. He regards the phenomenon as a case of radiation depend- 
ing on the molecular state of the radiating body. This may be compared 
with the case of platinum which, in its ordinary condition, is inactive on 
Phycorhyces , but, after exposure for a time to direct sunlight, will, without 
undergoing any apparent change, attract the filaments. 
Chemotropic Movements.§ — Dr. M. Mivoshi has carried out a series 
of experiments on the chemotropic movements of fungus-hyphae and 
pollen-tubes. The fungi experimented on were chiefly species of 
Mucor, Phycomyces , Penicillium, Aspergillus , and Saprolegnia ; also of 
Botrytis and Vredo. Certain chemical substances exercise either an 
attractive (positive) or a repulsive force^negative chemotropism) on the 
growing hyphse, thus greatly assisting their entrance into living 
organisms. The substances which produce the greatest effect are salts 
of phosphoric acid and of ammonia ; and next to them, extract of meat, 
peptone, asparagin, and grape-sugar. In contrast to the results with 
bacteria, nitrates and chlorides of potassium, sodium, and calcium pro- 
duced no effect. The irritating property of a fluid does not depend on 
* Landwirth. Versuchs-Stat., xlii. pp. 459-78. See Journ. Clicm. Soc., 1893, 
Abstr., p. 588. 
f Otvers. Finsk. Yet. Soc. Forhandl., xxxvi. (1894). See Nature, xlix. (1894) 
p. 466. X Cf. this Journal, 1893, p. 358. 
§ Bot. Ztg., lii. (1894) l te Abtheil., pp. 1-28 (1 pi.), and Flora, lxxviii. (1894) 
pp. 76-93. 
