314 My fJohnson's EiTperiments 



placed. But, instead of this, the plume, as it was gradually 

 protruded from the cotyledons, turned itself upwards, as usual 

 — and the radicle downwards. 



It might also be objected to this theory, that it does not at 

 all explain why these directions should be so exactly perpendi- 

 cularly upwards and downwards ; and there are others which, I 

 think, might be reasonably adduced. But I do not wish to 

 extend the present essay, by offering arguments, which are far 

 less satisfactory than the results of the foregoing experiments. 



II. The following experiments and remarks apply to the theory 

 of Mr Knight, which attributes the effects in question to the 

 agency of gravitation * ; a theory which is most ably supported 

 by his most ingenious reasonings and experiments. 



ExpEU. III. — A small iron-wire ring, on which was stretched 

 some net, was fixed in the mouth of an ale-glass. It was placed 

 about an inch below the brim, and the space above it being filled 

 with mould, several mustard seeds were sown in it. This ex- 

 periment, several times repeated, has given the following re- 

 sults. The radicles having penetrated downwards through the 

 net, have grown more or less directly downwards into the space 

 below this ; but they have never attempted by turning upwards 

 to re-enter the soil, even though they have, in some cases, attain- 

 ed the length of half an inch. 



ExpER. IV. — The little apparatus mentioned in Experiment I., 

 being filled with soil, and some mustard seeds being sown in it, 

 and watered daily, afforded, in repeated trials, the following very 

 curious result. As soon as germination had commenced, the 

 radicles grew downwardsj and appeared at the lower surface 

 of the net. But, no sooner had they penetrated through this, 

 than, instead of continuing their ordinary direction, as in the 

 former experiments, having just attained a length of about one- 

 eighth of an inch, they invariably began to turn upwards, endea- 

 vouring to regain the soil, often creeping along its under sur- 

 face, or even perforating the net two or three times ; and only 

 those newly protruded growing straight downwards -f-. 



• Phil. Trans. 1806. 



\ The same ultimately took place with the radicles mentioned in experi- 

 iuent I., after they had got out of the soU ; in every one there was some ap- 

 parent effort to turn towards the net. 



