686 SUMMARY OF CURRENT RESEARCHES RELATING TO 



mena of digestion observed in Nepenthes were probably due to enzymes 

 secreted by bacteria. E. Labbe has found something of the same kind 

 in Drosera, though here the bacteria play only a secondary part. Moulds 

 such as Aspergillus glaucus, PenicilUum glaucum, Mucor Mucedo, and 

 Gladosporium herbarum, with a few bacteria, were found to be present. 

 They provoke fermentation of the sugar secreted by the glands of the 

 plants, and give origin to certain acids. A proteolytic ferment which 

 peptonised fibrin was found in the secretion. 



Mycorhiza and Nitrogen Assimilation.* — A. Moller has recently 

 conducted experiments with seedling pines to determine whether the 

 mycorhiza of the roots could make use of the free nitrogen of the atmo- 

 sphere in the absence of other sources of supply. He grew plants in a 

 soil free from nitrogen, and others in soil supplied with saltpetre. The 

 latter grew much more vigorously, and an examination of the products 

 of each set of plants gave these a great preponderance in weight, amount 

 of nitrogen, etc. Moller considers that his results prove that myco- 

 rhiza does not assimilate free nitrogen. 



Irritability- 



Hygroscopicity as a Cause of Physiological Action at a Distance.! 

 The late Professor L. Errera chose Phycomyces nitens to study what 

 Elving had called a " new ' tropism ''depending on a strange and unknown 

 force." Phycomyces was chosen for experiment on account of its sensi- 

 tiveness : it is negatively geotropic, positively heliotropic, negatively 

 hydrotropic and thermotropic, and positively hapto tropic. Errera found 

 that the unknown agent which attracts or repels is simply water vapour ; 

 and three factors have to be taken into account : the energy, duration, 

 and quickness of absorption. A great number of substances were used 

 in testing the hydrotropism of the plant, including metals, salts, acids, 

 and organic substances, and the results of the experiments are given. 



Chemical Changes. 



Action of Insoluble Substances in Modifying the Effect of 

 Deleterious Agents.}: — The research on this subject undertaken by 

 Ruby Fitch is a continuation of work done by Nageli, who discovered 

 the hurtful influence of minute quantities of poison in water cultures of 

 plants, and who proved further that the poisonous effect could be 

 neutralised by the introduction of insoluble substances such as granite, 

 cotton-fibre, etc. The writer of this paper experimented with Aspergillus 

 niger and PenicilUum glaucum ; sand, glass, filter-paper, and porous clay 

 pipes were the insoluble substances ; copper sulphate and sulphuric acid 

 were the toxic agents introduced into the culture media. Exact tables 

 of results are given, but generally the results agreed with those of Nageli, 

 and these insoluble substances (sea-sand was the most effective) " acted 

 as agents of dilution or absorption, removing in some way poisonous 

 molecules or ions." 



* Ber. Deutsch. Bot. Gesell., xxiv. (1906) pp. 230-3. 



t Recueil Inst. Bot. (de Bruxelles) vi. (1905) pp. 301-66 (5 pis.). See also 

 Bot. Centralbl., cii. (1906) pp. 215-17. 

 % Ann. Mycol., iv. (1906) pp. 313-22. 



