Rothamsted Symposium on Trace Elements 118 



de ces Elements. En faisant varier la concentration du magne- 

 sium dans des milieux differant par leur teneur en rubidium, on 

 trouve en effet que le taux de rubidium modifie I'activit^ du mag- 

 nesium, dans des proportions analogues aux modifications de cette 

 activite qui sont apport^es par des variations de teneur en potas- 

 sium. Par exemple, lorsque la concentration en rubidium est 

 egale k 4,05 mgr et 8,1 mgr pour 100 cc dans des milieux exempts 

 de potassium, le coefficient d'action du magnesium est respective- 

 ment ^gal a 2 et 3,6 (Figure 23). 



Bibliographie: — Lavollay: Etudes sur rintervention du magnesium . . . (Th. 

 Fac.Sc, Paris, 1936, Hermann). — Lavollay et Laborey: C.R.Ac.Sc. 204:1686, 

 1937; C.R.Ac.Sc. 208:1357, 1939; C.R.Ac.Agric. 34:787, 1948. — Laborey, La- 

 vollay et Neumann: C.R.Ac.Sc. 212:624, 1941. — Javillier, Lavollay, Laborey 

 et Neumann: C.R.Ac.Agric. 27:398, 1941. — Laborey: Etudes experimentales sur 

 les courbes de poids d' Aspergillus . . . (Th. Fac.Sc, Paris, 1942). — Lavollay: 

 Rapports entre le phosphore et les autres elements ... (Le Phosphore en Biologie, 

 Presses Univ., p. 87, 1949). 



Points from Discussion of Paper hy Prof. Lavollay 



Dr. Gisiger:— 



Prof. Lavollay has raised a question of great practical im- 

 portance. We have soils in which with a minimum of nutritive 

 elements maximum growth of plants is obtained. We have imag- 

 ined that by the giving of a nutritive element in excess the har- 

 mony is destroyed and ought to be balanced by adding one or 

 several nutritive elements. Mitscherlich has demonstrated to 

 you in his 2nd law that the relations of the different nutritive 

 elements have an influence on the coefficient of activity. 



Prof. Burstrom:— 



The relationship between external concentration and growth 

 involves two processes: nutrient absorption and nutrient activity 

 inside the plant. Can you decide whether the magnitude of co- 

 efficients depends more upon the second than on the first process;" 

 In most cases we have a luxury consumption of the nutrient. Do 

 you know if your formula is valid also for a nutrient, of which 

 there is no luxury consumption, e.g. nitrogen? 



Dr. Lavollay:— 



Oui. Le coefficient d'action du magnesium est, dans une cer- 

 taine mesure, independant de la concentration en azote nitrique; 

 au contraire, ce coefficient varie avec la concentration de I'azote 

 ammoniacal. 



