224 SCIENCE PROGRESS 



are produced which greatly accelerated the growth of maize 

 seedlings in water cultures, even though only added in small 

 amounts. Experiments have now been performed (Proc. 

 Roy. Soc. B., vol. lxxxix. 191 7, pp. 481-507) to test the effect 

 of extracts of peat, thus treated, on the growth of Lemna minor. 

 When the aqueous extract of " Bacterised peat " was added to 

 a Detmer culture solution the rate of growth of the Lemna was 

 twenty times more rapid than in the control, whilst the increase 

 in weight was augmented 62 times. A less marked effect was 

 obtained by the addition of water extract freed from humic 

 acid. 



Miss Mockeridge {ibid. pp. 508-533) has tested the effect of 

 these extracts upon the activities of nitrifying and denitrifying 

 bacteria. She arrives at the conclusion that the activities of 

 the former are accelerated, whilst those of the latter are de- 

 pressed. Both investigators found that the alcoholic extract 

 and the phosphotungstic fraction produced similar results. 



Selected List of Recent Literature 



(Papers of which abstracts have been given are not included) 



BOWER, F. O., Studies in the Phylogeny of the Filicales, VI. Ferns showing the 



Acrostichoid condition with special reference to Dipterid Derivatives, Ann. 



Bot. January 19 17. 

 Brenchley, W. E., The Effects of Weeds on Crops, New. Phyt. May 1917. 

 Bristol, B. M., Life-history and Cytology of Chlorochytrium grande, Ann. Bot. 



January 1917. 

 Farrow, E. P., On the Ecology of the Vegetation of Breckland, III. General 



Effects of Rabbits on the Vegetation, Journ. oj Ecology, March 191 7. 

 Gano, L., Ecology of Florida, Bot. Gaz. May 1917. 

 Lotsy, J. P., Qu'est-ce qu'une espece ? Archives N/erlandaises de Set. Naturelles, 



t. hi. 1916. 

 Marshall, E. S., Critical Notes on some Britannic Saxifrages, Journ. Bot. June 



1917. 

 Shantz, H. L., Plant Succession on Abandoned Roads in Eastern Colorado, 



Journ. oj Ecology, March 1917. 

 Small, J., Floral Anatomy of some Composite, Journ. Linn. Soc. May 1917. 



PLANT PHYSIOLOGY. By I. Jorgensen, Cand. phil. (Copenhagen), 

 D.I.C. (Plant Physiology Committee), Imperial College of Science and 

 Technology, London. 



Carbon Assimilation. — Carbon assimilation, which for a few 

 years has not occupied a prominent position in plant physio- 

 logical researches, has again attracted the attention of many 

 workers. 



