( 196 ) 



this experiment in the following manner, see tig. 1. Of thin sheet- 

 aluminium a tlat balance-leam was made, 672 ^'m- long, resting 

 with a brass cap on a steel poijil. On one end a Lathj'rus seed was 

 stuck, to the other a small bit of paraffin was melted, balancing 

 the seed. Exactly under the seed a small trough of mercury Avas 

 placed with very little water on the mercury. By another small 

 vessel, filled with water, and Iw a little bell-jar OAer the whole 

 arrangement, the air was kept moist. The root after a few days grew 

 down 7 mm. into the mercury, vrithout the balance being lifted. By 

 adding to it and by melting away from it, the small bit of parai'tin 

 w^as occasionally brought into equilibrium with the growing seedling, 

 after the latter had been dried with filtering paper. The upward 

 pressure of the mercury which amounted to more than 100 mg., 

 was now l)alanced by the surface-tension of the water, raised by 

 capillarity. It might even have been a great deal more, for on the 

 other arm of the balance 1 couhl slill jjlace about 100 mg. in addition 

 to the bit of paraffin before the i)lantlet was lifted out of the mercury. 



We can now explain why various investigators could give such 

 totally contradictory reports. 



In the first place we may trust Pinot's results (1829). The 

 description of his experiments gives the imprcssioji that he observed 

 accurately. 



DuTROCHET (1829) iHd not re|)eat the exi)eriments with the perse- 

 verance which is necessary to obtain a good I'esult. 



The experiments of Mulder (1829) were too coarse and \'alueless 

 for Pinot's problem. Of Goeppert (1831) the same may be said. 



Payer (1844) used a slice of cork or a i)lug of cottonwool on a 

 thick layer of water, so that later writers wrongly always mention 

 PiNOT and Payer together. His experiment, described above, with a 

 laver of mercury abo\'e a layer of water, is ingenious. I repeated 

 it, using lacquered iron-gauze instead of platinum-gauze. The roots 

 of seeds of Lathyrus and Phaseolus, stuck on pins in corks, grew 

 very finely through the mercury into the water ; see fig. 2. The 

 mercury is indistinct in the figure because of the patch of muslin 

 which lies on the gauze. It was namely pushed downwards in the 

 glass trough in order to show the seeds stuck on the pins. 



Payer stated that the roots did not penetrate again into the mer- 

 cury once they had been taken out of it. Pinot and Wigand asserted 

 the contrary. This can easily be explained. The latter left the seeds 

 free indeed and the surface-tension acted as before when the plant 

 was replaced in the mercury in its former [)Osition. Payer's seedlings, 

 on the other hand, were fixed ; they penetrated into the mercury 



