964 AGRICUI/rURAI, BOTANY, ClIKMISTRV AND I'lIVSIOLOGY OF PI.ANTS 



radical. Any one of these salts causes the immediate separation of a littl' 

 calcium, which increases as the action is prolonged, and finally represent-, 

 a considerable proportion of the total weight of calcium in the plant. 



It is not only calcium which is thus exijelled from living plants by any 

 other metal present in the state of saline solution. For instance, potassium 

 is also separated on treating the plant with a calcium salt. Thus the cycle 

 is complete for all alkaline or alkaline-earth metals. The calcium in plants 

 is expelled by the salts of other metals, but the other metals are expelled by 

 the salts of calcium. It is a perfectly reversible phenomenon, in wliich the 

 action of the most abundant salt preponderates. 



There is a remarkable similarity between the absorbent properties of 

 the soil for saline solution and those exhibited by living plants. In both 

 cases the fixation relates mainly to the bases, and these bases can expel 

 each other reversibly. This forms the direct demonstration of a contention 

 put forward by the writer in 1904; " the pectose in the walls of root hairs 

 being in close contact with the particles of the soil, the whole together, soil 

 and walls, forms a colloidal system having the same properties of absorp- 

 tion everywhere. The bases are not held and kept in reserve in the soil 

 but also in the cell wall within immediate reach of the protoplasm ". 

 Indeed there is nothing to show that the cell content itself does not take part 

 in the exchanges, and this simple hypothesis shows the importance which 

 may attach to the study of these reversible exchanges in living tissues. 



745 - The Relations between the Presence of Magnesium in Leaves and the Function 



of Assimilation. — Andr6 G., in Comptes Rendus de V Academic des Sciences, Vol. 162, 

 No. 15, pp. 563-566. Paris, April 10, 1914. 



Several authors have proved that crude chlorophyll, extracted from 

 leaves by alcohol or benzene always furnishes an ash in the composition 

 of which magnesium phosphate predominates ; other more recent work has 

 also shown that magnesium is the only fixed element forming a part of the 

 molecule of chlorophyll ; finally, Mi,i,E Mameli demonstrated that the 

 quantity of pigment forming in the assimilating organs is related to the 

 weight of magnesium supplied to the plant. 



If magnesium plays so special a part in the molecule of chlorophyll, 

 it might be expected that the weight of this element would be greater in 

 proportion as the process of assimilation reaches greater intensity in the 

 plants from which it is extracted. The writer therefore, at different vege- 

 tative periods, detached a number of leaves from different species of plants, 

 dried and crushed them, afterwards extracting them by heating with ether 

 and afterwards with alcohol. He measured the magnesium and phos- 

 phorus in the product of the extraction. He thus determined the weight 

 of phosphorus (reckoned as H3PO4) and of magnesium (reckoned as 

 MgO) contained per 100 grams of substance dried in vacuo at the differ- 

 ent times : i) in the part of the leaf substance dissolved in the ether and 

 alcohol [organic pho.sphorus and magnesium); 2) in the part not dissolved 

 [residual phosphorus and magnesium). 



From the table giving these figures, and also the relations between or- 

 ganic phosphorus and residual phosphorus on the one hand and organic 



