( J05 ) 



niiisl l)c exioiidcd jiloiii;' llio wliolo niari;iii. '\l\o ('.iiiillarv ('(tiisjaiil 

 of water is 8,8, lioiice for cacli iiini. of (lic cii-ciiinrcM-ciicc of (lio 

 raised water a force of 8,8 nig', is iKM-cssary. 



This circumference measures with (lie swollen m^viI of «garden-cress 

 14 nnn., w i(!i Ladiyi'us al)ou( 21) mm., so (jia( a force of more than 

 100 mg'. is available for compensating diiferences of iipwai'd pres- 

 sure and weight. 



Therefore it is necessary however (hat the seed oi- piantiet cannot 

 capsize too easily. The capsizing is a rotation round a horizontal 

 axis by wdiich the water-surface need not be increased. The \'ertical 

 component of the surfjice-tension is consequently of no etfect to jirevent 

 the piantiet from being upset and hence being lifted out. This rotation 

 is rendered more difficult by water, rising by capillarity between 

 two seedlings that lie close together, or between the glass and the 

 seedling, because this water has a greater horizontal surface which 

 must be increased during the capsizing. Hence it is against (he glass 

 wall that the roots penetrate most frequently, in which case also the 

 friction between wall and root facilitates the penetration by the 

 unilateral horizontal i)ressure of the mercury. 



The thinner the layer of water, the closer the centres of surface- 

 tension and upward pressure lie together and the shorter is also the 

 lever-arm with which a lateral component of the hydrostatic pressui-e 

 acts on a somewhat slanting radicle in order to upset the piantiet. 

 With a seed in an entirely free position, ])eneti"ation will be })ossible 

 but in the most favourable case only an unstable equilibrium will exist. 

 The penetration of freely placed seeds will consec(ucntly be generally 

 absent, not because the upward pressure soon excee<ls the weight of 

 the little plant, but because the plant is overturned by rotation. 



PiNOT immediately obtained such a good result because his mercury- 

 troughs were so small, only one centimetre broad. So I also re[)ea(ed 

 the experiments in (his way. Of a glass tube of one cm. diameter 

 bits Nvere cut oif and closed at (he bottom with a cork. These troughs 

 \verc filled with mercui-y and in each a soaked seed of Tiathyrusor 

 garden-cress was put \\i(h as li((le wa(er as possible. 'i'!:e \va(er (hat 

 was raised by capillari(y now stuck the seed against (he glass wall 

 and (he root i)enetrated more easily Itecanse it was less easily 

 upset. When I |)laced the seeds with the radicle turned towards the 

 centre of (he (rough, i( grew doA\ ]i in(o the mercuiy itself, not between 

 the glass wall and the mercury. 



I'lXOT used still anothei' and elfectivc means (o prevent capsizing 

 and a( the same time to eliminate the weight of (he seed, viz. by 

 the experiment with (he silver needle, described above. I repeated 



