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ADVENTURES IN RADIOISOTOPE RESEARCH 



<'' The fruit was removed when the plant was introduced into the culture solution, since it constitutes 

 a particularly good nutritive medium for troublesome moulds. 



of the lead content taken up by the root from a lO"^ N solution: 61.2, 

 62.3, 57.4, 59.6, 55.4, 57.8, 47.3, 62.2, 61.7, 62.6, 60.0, 51.2, 68.7, 57.6. 

 From the above experimental data it is seen that, whereas in the case of 

 a 10~^ N solution more than half of the lead is taken up by the root, the 

 percentage loss when a 10"^ solution is used only amounts to 0.3, although 

 the quantities of lead taken up by the root in the latter case are very 

 much greater than in the former case. It is of interest to note that the 

 percentage of lead which passes over into the stem and leaves from the 

 concentrated solution of lead is not smaher than that from dilute solu- 

 tions. This can be interpreted as meaning that with very dilute solutions 

 the root itself is able to bind almost the whole quantity of lead, and thus 

 renders extremely difficult the ascent of lead into the stem and leaves. 

 On the other hand, when a concentrated lead solution is used, an ample 

 sufficiency of unbound lead is available, and this can be carried upwards 

 by the transpiration current. Except in the case of concentrated solutions, 

 the root thus protects, as it were, the remaining parts of the plant, and 

 this marked ability for "binding" lead is probably connected with an 

 explanation of the relatively small toxicity of lead for plants, discussed 

 on p. 444(^> [cf. Strasburger, 1891]. 



(1^ Trees placed in solutions of copper sulphate or picric acid, etc. do not die 

 until the poisonous substance has reached the highest points of the crown. 



