Mr Johnston's Ecfperiments on the Germination of Plants. 313 



sides of this hoop so formed, HE |H 



three slender iron-wire legs ^|L- -^^1 



were fixed, as here represented. I cf 



To the lower surface, a, a, a, I 



some thread-net was stitched, / 



and the space above this being / 



then filled with moistened soil, "'^" ' 



nine mustard-seeds, which had already protruded their radicles, 

 being procured, the latter were pushed gently upwards (i. e. 

 through the net) into the moistened soil,at its lower surface, a, a,a. 

 Eight of these lived, and grezv downwards, so as to become 

 hooked in the meshes of the net. See note on Experiment 4. 



ExPER. II. — A common horse-bean, having a very straight 

 radicle, and already about an inch long, was fixed securely at 

 the bottom of a glass, in such a manner that the radicle pointed 

 directly upwards. It was then completely covered with water. In 

 a few days the radicle became considerably curved downwards., 

 and the plume, having now grown out, had directed itself iip- 

 wards. 



1st, It is remarked by Mr Keith*, and I think very justly^ 

 that, according to this theory of Dr Darwin, the radicle, if 

 lodged in an insulated mass of mould, and in an inverted posi- 

 tion, ought certainly to elongate itself in that direction, perpen- 

 dicularly upwards, instead of downwards. 



In the first experiment above described, I believe these con- 

 ditions were exactly fulfilled — yet the result was far different : 

 for, instead of continuing to grow in the direction in which they 

 were placed, they immediateli/ turned downwards. But, if the 

 radicle grew downwards in ordinary circumstances, because it is 

 " most excited" in that direction, by the moist earth beneath, — 

 in this experiment it ought surely to have grown upwards, for 

 here the moist soil was placed above. 



9.dly, In Experiment II, if the contact of air with the plume' 

 was not entirely prevented (as the water would contain some), 

 it must, at least, have been equally stimulated by air on every 

 side, and ought therefore to grow as readily in one direction as 

 in another : and the radicle, surrounded as it was on every side, 

 and therefore equally " excited ^ in every direction, might be 

 expected to continue its growth in any position in which it was 

 • Sjst. of Physiolog. Botany, vol. ii. p. 25. 



