302 Blackman . — Radio-activity & Normal Physiological Function . 
In view of the fact that potassium is an essential constituent of the 
plant, these results are clearly of great importance to botanists ; it may be 
that the importance of potassium in the life of the plant may in part be 
explained by its radio-active power. In the minuteness of the dose of the 
heavy radio-active elements required compared with that of potassium, 
and in the ease with which a toxic concentration is reached, may be the 
explanation of the conflicting results obtained by the addition of radio-active 
earths to soil. In any case, however, Zwaardemaker’s result would in no 
way suggest the superiority of such earths over simple potassium fertilizers. 
Physiologists will welcome the deeper analysis of biological processes 
which Zwaardemaker has achieved, yet it must be admitted that they 
increase still further the difficulty of envisaging his subject which faces the 
worker in the field of either animal or plant physiology. To the equipment 
of ordinary physics and chemistry which such a worker should bear has 
been added of late years a knowledge of many aspects of physical chemistry, 
of colloid chemistry, and of some of the more special branches of electrical 
science ; to this heavy burden must now be added a knowledge of radio- 
active phenomena. 
Imperial College of Science and Technology, 
London, S.W. 7. 
