206 



W. GARDINER ON AURORA. 



periment was tried with colourless roots ; but no alteration in their 

 direction was produced. From this it appears evident that colour is 

 one of the conditions that determine the directions of vegetables and 

 their parts towards the light, and consequently towards the sky. 

 This is so true, that colourless stems are known to assume the di- 

 rections of roots. In the Sagittaria sagittifolia, this is particularly 

 obvious. Shoots are produced from the axillee of all the radical 

 leaves which grow at the bottom of the water. These shoots have 

 their points directed towards the sky, like those of all vegetables. 

 The young stems, which are produced by these shoots, are entirely 

 colourless, like roots ; and, instead of taking a direction towards the 

 sky, as coloured stems would do, they lead downwards, pointing 

 towards the centre of the earth. In order to take this position, the 

 young shoot forces its way through the substance of the petiole which 

 covers it ; thus overcoming a mechanical obstacle in its tendency 

 towards the earth. This subterranean stem next takes a horizontal 

 course, and does not assume any tendency towards the sky, until the 

 points become green. I have also remarked a similar phenomenon in 

 roots. It is well known that exposed stems of many plants, produce 

 roots ; when green, they turn upwards, as in Pothos and Cactus phyl- 

 lanthus ; when colourless, they point downwards. Hence, it is to be 

 inferred, that stems do not descend merely because they are stems, 

 but because their parenchyma is coloured; and that Toots descend, 

 not in their quality of roots, but because their parenchyma is colour- 

 less. It seems, however, that although this law is uniform in its 

 operation in all terrestrial plants, yet that a deviation, or apparent 

 deviation from it, exists in the parasitic miseltoe. The radicle of this 

 plant, which is of a paler green than the other parts, instead of turn- 

 ing towards the light, avoids it with so much pertinacity, that it is 

 impossible to induce it to take such a direction ; so that it seems to 

 be repelled by light. 



STORMS PREDICTED FROM THE AURORA BOREALIS. 



BY MR. WILLIAM GARDINER, JUNIOR, OF DUNDEE. 



I feel much pleasure in being able to communicate a fact or two 

 respecting the atmospheric changes indicated by the appearance of 

 the Aurora Borealis, corroborative of these adduced by Captain Winn, 

 at page 108. 



