SECTIONAL TRANSACTIONS.— K. 495 



Breaking the connection between aleurone layer and the endosperm 

 before the grain is soaked has the effect of reducing the growth rate of 

 embryo, while breaking the connection after the grain has been soaked has 

 no effect on the embryo. 



Mr. E. K. Woodford and Prof. F. G. Gregory. — The relation of oxygen 

 supply and respiration rate to anion and cation absorption by barley 

 plants at varying nutrient levels (3.15). 



An apparatus is described for measuring simultaneously nutrient absorp- 

 tion and root respiration rate, at varying oxygen tensions and under aseptic 

 conditions. 



The results of an experiment are presented in which sixteen combinations 

 of oxygen tensions and nutrient concentrations were studied. Special 

 care was taken in the design of the experimient so that the interaction of the 

 factors could be statistically estimated. 



A considerable absorption under completely anaerobic conditions was 

 found for nitrogen, phosphorus, and potassium. With phosphorus, 

 absorption in pure nitrogen was considerably greater than in 20 % 

 oxygen. Nutrient concentration' was the chief factor in absorption, irre- 

 spective of oxygen concentration. Respiration was scarcely affected by 

 nutrient concentration but was greatly increased by increasing the oxygen 

 tension. Oxygen supply scarcely affected absorption at low nutrient levels 

 but had a large effect at high concentrations. This is the chief interaction 

 noted. 



Respiration has no direct relation to nutrient absorption in experiments of 

 short duration, where root growth plays no part. 



In excised root systems the rapid fall in absorption precedes the fall in 

 respiration rate. 



The relation between absorption and nutrient concentration is different 

 for anions and cations, and specific effects of ions were observed also in the 

 relation to oxygen tension. 



Mr. G. J. BoswELL and Mr. G. C. Whiting. — The catechol oxidase 

 system (3.45). 



By the use of an oxidation product of catechol as an inhibitor of cell 

 respiration it has been possible to show that the catechol oxidase system 

 controls not less than 65 % of the total oxygen uptake and carbon dioxide 

 output of thin slices of the potato tuber. The amount of the residual 

 respiration is at a maximum, 33 %, in potatoes collected and used during 

 September and October and decreases to a minimum value of about 10 % 

 in potatoes stored in the autumn and used experimentally in the following 

 April and May. 



Semi-popular Lecture by Prof. A. H. R. Buller, F.R.S., on The 

 sexual process in the rust fungi {e^.o). 



During the past twelve years J. H. Craigie, A. M. Brown, and other 

 workers in the Dominion Rust Research Laboratory at Winnipeg have 

 investigated the sexual process in the rust fungi by means of experiment. 

 As a result of their labours we now know that, in long-cycled heterothallic 

 rust species, there are two ways in which the sexual process is normally 

 initiated : (i) by the fusion of a (+) mycelium with a (— ) mycelium, as 

 first observed by Craigie (1927) in compound pustules oi Puccinia helianthi 



