( lit4 ) 



and turiicMl brown. The purifK'ation took place with diliile iiitnc acid. 



In these experiments some roots had so far grown down that 

 weight alone conld not explain this. My radicles did not go down 

 so deep as those of Wigand ilOwe^■e^. Now it soon became clear 

 ill what respect the plantlets that had grown into the mercuiy were 

 distinguished from those which had not. They were not quite 

 free, namely, but lay against another seed ; round and between both 

 seeds the water had risen through capillarity and gave some support 

 to the seed by the tension of its concave surface. The molecular 

 forces of the water thus opposed the upward pressure of the mercury. 



DuRAND calculated the force \vitli which the mercury forces seedlings 

 of Lathyrus odoratus upwards. For a cyHudrical ra(Hclc of ^1^ mm. 



diameter this force amounted per mm. length to -t ~ Xl'J'ö = () 



milligrammes; for a length of 20 mm. this is 120 milligrammes. 



The volume of the radicles can be approximately determined from 

 the length and the thickness in various places; or by weighing the 

 cut off radicles. (The specific gravity is about one). 



The tapering of the roots tctwards the top makes the determination 

 of the volume from measurements of thicknesses rather inaccurate. 

 For approximate values the two methods supplement each other 

 sufliciently, however. 



For radicles of Lathyrus of .5 to 7 mm. leiiglh I found volumes 

 of 5 to 8 mni\ ; the upward pressure of the mercury is then 68 to 

 'iOO nig. The Lathyrus plantlels weighed about 200 mg. 



Jloots of garden-cress of 5 to U mm. had volumes of 1 to 2 mm\; 

 the upward pressure is then 14 to 27 mg. The cress i)lanllcls weighed, 

 before the sccdcoat liad fallen off, about 17 mg., after the falling 

 off, 8 mg. '). 



The weights of the jtlauilets are considerably' diniinislied, however, 

 by their lying in the water with parts that are much more \oluininous 

 than the radicle. When the u[)ward })ressure of the layer of water 

 has been subtracted, the weight that must be comjiared to the upward 

 pressure of the mercury remains. In the case of Lathyrus this 

 weight will still be in excess, but with garden-cress there is a greater 

 or smaller deficiency. For the greater depths of Pinot and Wigand 

 this deficiencv becomes greater still, but its amount remains small 

 and can easily be comiiensated by the molecular forces of the water. 

 If the seedling be raised through a very small distance, the surface 

 of the water that has been raised against the seed by capillarity, 



1) The c.'ist off sccdcoat alone wciglis about IG mg., evidently because it is 

 filled with water, lelained ])y capillaiity. 



