Royal Society of London. 365 



to two wheels, one of which was horizontal, and the other 

 vertical, turned by a rivulet that runs through his garden. 

 One of these wheels performed 150 and the other 250 

 rotations in a minute ; a velocity which rendered the power 

 of gravitation equal on both ^ides of the seed, and pro- 

 duced, as the author had expected, the protrusion of roots 

 and elongation of germs in all directions. From several 

 very decisive experiments to elucidate this fact, he con- 

 cludes, contrary to Du Haniel, that gravitation is the sole 

 cause of the descent of roots and ascent of germs, and that 

 both diverge in all directions when under the influence of 

 equal pressure. His observations also refute the too com- 

 mon notion that the roots of plants have an affinity for 

 water, or rather that water attracts them from their accus- 

 tomed direction by the nutriment which it affords. Mr. K. 

 confirms, however, fhe generallv received opinion of the 

 affinity of plants for light. On the reputed tap-root of 

 oaks he observes, that, after examining above 2000 trees, 

 not one of which had such a root, he thinks he shall be 

 pardoned for concluding that it has no existence. Of these 

 interesting experiments we shall only observe, that, al- 

 though the naturalist has carefully noted the time taken bv 

 the different seeds to germinate in the horizontal and ver- 

 tical wheels, he has not mentioned what time would have 

 been necessary for the same purpose in similar earth sub- 

 ject to the usual effect of gravitation. Such a comps^risoa 

 made with seeds of all the diflerent qualities capable of ve- 

 getating, might develop some facts important to our pre- 

 sent system of husbandry. On the same evening also com- 

 menced the reading of a " Third Communication on Arti- 

 ficial Tannin, by Mr. Hatchett."^ 



January 23, the right honourable the President in the 

 chair. Continuation of the above communication. Mr. 

 Halchett found that all gums, resins, and balsams, yield 

 this artificial tanning substance on being treated with nitric 

 acid, as observed in iiis preceding papers. It appears that 

 all these substances yield at one operation a certain quantity 

 of this matter ; but if tbe process be continued too long 

 the product is destroyed, the same as the natural tannin is 

 by nitric acid. Mr. Hatchctt was not able to ascertain 

 either the specific quantity produceablc at once, nor the 

 precise time requisite to disenszage the greatest possible 

 quantity without injuring the entire product. The autlior, 

 animated with this complete success on resinous substanct-A, 

 has pursued ))is researches on a vast variety of vegetable 

 productions ; whence it appears, that-almost all vegetablea, 



after 



