316 Mr Johnson^s Experiments 



On these experiments I now make a few observations. 



1. The remarkable difference in the results of experiments III. 

 and IV. (a difference of which words alone convey, I fear, but an 

 imperfect idea), can I conceive only be attributed to this circum- 

 stance, in which alone they were not analogous, viz. the presence 

 in the one case, and the absence in the other, of moisture below 

 the net. In experiment III. the radicles, when protruded, had 

 to grow into the lower part of the glass, where they were sur- 

 rounded with moist air. Whilst in experiment IV., from the con- 

 struction of the apparatus, a current of dry air would be freely 

 admitted to them. In the one case the radicles continued to 

 follow their ordinary direction downwards^ in the other they 

 instantly began to tend upwards. 



I infer, that, in the former case, the radicles grew as usual 

 downwards, because sufficiently supplied with moisture (not 

 that moisture is by any means the cause^ in the way Dr Dar- 

 win supposes); but in the latter, becoming sensible, in some un- 

 known way, of the want of this necessary nourishment, they 

 instantly began to make efforts to obtain it by turning upwards. 

 But if they can thus, when their necessities require it, turn up- 

 wards in direct opposition to their ordinary course, and to the 

 power of gravity, they must surely be endowed with some force 

 different from, and more powerful, than that of gravitation. 



2. Having thus found that the radicle of a seed was capable 

 of turning itself upwards, and in opposition to gravity, it was 

 my object to learn if its direction might not also be totally in- 

 verted by the same means ; having effected which, by centripe- 

 tal motion, seems to be the principal fact on which Mr Knight 

 founds his theory. The result of the 5th experiment shews 

 that this is possible. 



3. It is, I think, evident, from these experiments, that al- 

 though a radicle, when first protruded, endeavours always to go 

 downwards (even if surrounded with water), it is, nevertheless, 

 when its necessities require it, capable of exerting some 

 power by which its direction is totally inverted ; and that as 

 this motion is directly contrary to the agency of gravity, the 

 power of the radicle which overcomes it must be greater, and 

 therefore distinct from it. It may, however, still be maintain- 

 ed by some, that the ordinary downward direction is owing to 



