234 PHYSIOLOGY OF NUTRITION. 



aspect, so that they are exposed to the sunshine and high tem- 

 perature. During this period the soil in the pots is not watered. 

 In experiments on the absorption of Lithium solution, plants 

 vegetating in food solutions must be removed from them imme- 

 diately before the experiments begin, and placed in a 2 per cent, 

 solution of Lithium nitrate. If, on the contrary, we work with 

 pot plants, the soil in the pots must be thoroughly soaked with a 

 2 per cent, solution of Lithium nitrate. The plants are now left 

 exposed to very favourable conditions for transpiration. At the 

 end of an hour we sever each of the stems above the soil, cut it 

 up from above downwards into small pieces, and cut oil the leaves. 

 In these operations great cleanliness is necessary in order to avoid 

 conveying the Lithium salt which may be present in one part of 

 the plant, by means of the knife, to another part. To test for 

 Lithium, thin pieces of the stem or small pieces of leaf are taken 

 by the forceps and held in a glass flame, towards which the 

 spectroscope is directed. Larger quantities of Lithium can be 

 recognised immediately, smaller quantities only when the ash 

 glows. To avoid obtaining too high a value for the height to 

 which the Lithium salt (and therefore also the water) ascends, we 

 must always reckon the distance of the highest part of the stem 

 or highest leaf in which| Lithium is detected, only from the root- 

 neck [collum]. It is also frequently a good plan not to decapitate 

 the plant, but simply to cut off pieces of leaf after the experiment 

 has proceeded for a certain time, and test these for Lithium. It 

 is worthy of observation that we can sometimes recognise con- 

 siderable quantities of absorbed Lithium in the leaves of the plants 

 when it is not to be detected in the lower parts of the stem, a fact 

 of which I satisfied myself in testing Sachs' method for deter- 

 minating the rate of water conduction in plants. Often the 

 Lithium obviously accumulates in the leaf tissues in larger quan- 

 tities than in the stem. Sachs made the following determinations 

 of the height to which water and Lithium salts ascend in plants. 



Ascent per hour. 



Salix fragilis 85 cm. 



Zea Mais . . . . . . 36 ,, 



Nicotiana Tabacum . . . . 118 ,, 



Cucurbita Pepo . . . . 63 ,, 



Helianthus annuus . . . . 63 



Recently experiments with pigment solutions for determining 



