218 



in alcohol, a partial solution is formed, leaving an elastic substance, 

 which is said to possess the properties of caoutchouc, but which be- 

 comes hard by exposure to the air. 



The author has remarked, that the portion of mastic dissolved in 

 the alcohol may be precipitated from it by water, and that this pre- 

 cipitate possesses the properties of a pure resin ; but when a stream 

 of oxymuriatic acid gas was passed through the solution, a tough 

 elastic substance was thrown down, which became brittle when dry: 

 this precipitate was soluble in boiling alcohol, but separated from it 

 as the solution became cool. Its properties, therefore, approached 

 in some measure to those of the original insoluble part. 



On the Direction of the Radicle and Germen during the Vegetation of 

 Seeds. By Thomas Andrew Knight, Esq. F.R.S. In a Letter to 

 the Right Hon. Sir Joseph Banks, K.B. P.R.S. Read January 9, 

 1806. [Phil. Trans. 1806, p. 99.] 



It is, Mr. Knight observes, very well known, that in whatever 

 position a seed is placed to germinate, its radicle always makes an 

 effort to descend towards the centre of the earth, whilst the elon- 

 gated germen takes a precisely opposite direction : and it has been 

 proved by Du Hamel, that if a seed, during its germination, be fre- 

 quently inverted, the points, both of the radicle and germen, will 

 return to their first direction. These opposite effects have, by some 

 naturalists, been attributed to gravitation; and Mr. Knight con- 

 ceived, that if they really proceeded from that cause, those effects 

 would take place only whilst the seed remained at rest, in the same 

 position with respect to the attraction of the earth, and that the 

 operation of gravitation would be suspended by a constant and rapid 

 change of position in the germinating seed, and might be counter- 

 acted by the agency of centrifugal force. In order to determine 

 how far the above opinion was well founded, he made the following 

 experiments : 



Having a strong rill of water passing through his garden, he con- 

 trived, by its means, to give motion, vertically, to a wheel of eleven 

 inches diameter. Round the circumference of this wheel, several 

 seeds of the garden-bean, which had been previously soaked in water, 

 were bound in such a manner that their radicles were made to point 

 in every direction. The wheel made rather more than 150 revolu- 

 tions in a minute. 



In a few days the seeds began to germinate, and Mr. Knight had 

 the pleasure to see that the radicles, in whatever direction they were 

 protruded, turned their points outwards from the circumference of the 

 wheel, and in their subsequent growth receded still further from it. 

 The germens, on the contrary, took the opposite direction ; and in a 

 few days their points met at the centre of the wheel. Three of these 

 plants were suffered to remain on the wheel ; their stems soon ex- 

 tended beyond its centre, but their points returned, and met again at 

 the centre. 



