18i SENSITIVENESS OF THE APEX Chap. IH 



them Bot quite perpendicularly downwards, were coLted with 

 the black grease for a length of from 1 to Ij mm. The sieves 

 were inclined at 30° with the horizon. The greater number of 

 these radicles were examined after 22 h., and a few after 25 h., 

 and within these intervals they had grown so quickly as to have 

 nearly doubled their lengths. With the ungreased radicles the 

 chief seat of curvature is at a distance of not less than between 

 3'5 and 55 mm., and not more than between 7 and 10 mm. from 

 the apex. Out of the 13 radicles with greased tips, 4 had not 

 moved at all towards the sieve ; 6 were deflected towards it and 

 from the perpendicular by angles varying between 10° and 35° ; 

 and 3 had come into close contact with it. It appears, therefore, 

 at first sight that greasing the tips of these radicles had checked 

 but little their bending to the adjoining damp surface. But the 

 inspection of the sieves on two occasions produced a widely 

 different impression on the mind; for it was impossible to 

 behold the radicles with the black greased tips projecting from 

 the bottom, and all those with ungreased tips, at least 40 to 50 

 in number, clinging closely to it, and feel any doubt that the 

 greasing had produced a great effect. On close examination 

 only a single ungreased radicle could be found which had not 

 become curved towards the sieve. It is probable that if the 

 tips had been protected by grease for a length of 2 mm. instead 

 of from 1 to Is mrilr, they would not have been affected by the 

 moist air and none would have become curved. 



Triticum vulgare. — Analogous trials were made on 8 radicles 

 of the common wheat ; and greasing their tips produced much 

 less effect than in the case of the oats. After 22 h., 5 of them 

 had come into contact with the bottom of the sieve; 2 had 

 moved towards it 10° and 15°, and one alone remained perpen- 

 dicular. Not one of the very numerous ungreased radicles 

 failed to come into close contact with the sieve. These trials 

 were made on Nov. 28th, when the temperature was only 4°'8 C. 

 at 10 A.M. We should hardly have thought this case worth 

 notice, had it not been for the following circumstance. In the 

 beginning of October, when the temperature was considerably 

 higher, viz., 12° to 13° C, we found that only a few of the 

 ungreased radicles became bent towards the sieve; and this 

 indicates that sensitiveness to moisture in the air is increased 

 by a low temperature, as we have seen with the radicles of 

 Vicia faha relatively to objects attached to their tips. But in 

 the present instance it is possible that a difference in the dryness 



