VITALITY AND GEBMINATION OF SEEDS. 191 



nature and varying character of the stimulus and to the 

 extreme difficulty of successfully controlling its application, 

 necessarily be extremely difficult. 



If Hemp and Peas are placed in a tube rilled with 

 boiled sterilized water and closed at the open end by a 

 loose plug of cotton wool it is commonly found that the 

 radicles of the seeds immediately, in contact with the 

 plug of cotton wool, grow upwards against the action of 

 gravity and finally emerge from the open end of the tube, 

 then growing vertically downwards. If the tubes are 

 kept slanted, at a small angle with the horizontal so as to 

 dimmish the antagonism between the geotropic and 

 oxy tropic irritabilities of the radicles, the upward curvatures 

 of these towards the source of oxygen and away from 

 parts where it is absent or deficient, are more markedly 

 produced. The effect might possibly partly be due to 

 somatotropism the radicles preferring rather to burrow in 

 the damp cotton wool than to immerse themselves in the 

 subjacent water. This error is, however, easily obviated by 

 filling the lower parts of the tubes with cotton wool soaked 

 in boiled sterilized and practically oxygenless water. Above 

 this the soaked seeds are placed and then covered by a loose 

 plug of cotton wool. For purposes of comparison similar 

 experiments are also made with tubes open at both ends. 

 Both sets of tubes are placed at a slight angle 15° — 

 30°, with the horizontal and kept in a moist well aerated 

 atmosphere at a temperature of 25°C. In the tubes, open 

 at both ends, the radicles unless affected by somatotropism 

 grow directly downwards, but in the tubes in which only 

 the upper end is open in most cases the radicles bend 

 upwards and may go on growing upwards against the 

 action of gravity until they reach the mouth of the tube 

 when they at once grow downwards. In many cases the 

 radicle after bending upwards for a short distance and 



