General Notices. 375 



tude to which its effects reach on the sides of the valleys is dependent on the 

 mean temperature of the day and night at the time of its occurrence : when 

 that temperature is high, the lower places only are affected by the frost ; but, 

 when low, the frost extends to much higher grounds. Hoarfrost occurs only 

 during a calm state of the air, and when the sky is clear ; but the stillness of 

 the air in the bottom of the valley is invariably accompanied by downward 

 currents of air along all the sloping sides of the valley ; and it is to this fact, 

 first noticed by the author, that he wishes more particularly to direct the 

 attention of the Society, as affording a decisive proof of the correctness of 

 the views he entertains, being in accordance with the theory of Dr. Wells. 

 He finds that after sunset, in all seasons of the year, and at all mean tem- 

 peratures of the air, and whether or not the ground be covered with snow, 

 whenever the sky is clear, although there may be a dead calm at the bottoms 

 of the valleys, currents of air, more or less strong and steady, run downwards 

 on the inclined lands, whatever may be their aspect with reference to the 

 points of the compass. These currents are the result of the sudden de- 

 pression of temperature sustained by the surface of the earth, in consequence 

 of rapid radiation, by which the stratum of air in immediate contact with that 

 surface, becoming specifically heavier by condensation, descends into the 

 valley, and is replaced by air which has not been thus cooled, and which, 

 therefore, prevents the formation of hoarfrost on the surface of these de- 

 clivities. (At/ienceitm, April 17. 1841.) 



Average Temperature at which Seeds will germinate. — I till my garden with 

 my own hands, and take great delight in it. It not only furnishes a whole- 

 some exercise, but it affords me a much relished mental recreation, in watch- 

 ing the curious developements of the vegetable world, its recuperative powers, 

 and, indeed, its pathology and physiology generally. Part of the experiments 

 which I have made are intended to show at what average temperature at noon 

 various seeds will germinate, and how many days are requisite for them to 

 vegetate at any given temperature. Thus, I find that the Lima bean, at a 

 temperature of 83° (in the shade) will appear above ground in seven days;^at 

 a temperature of 62° it requires twenty days. The marrowfat pea, at 51°, re- 

 quires nineteen days ; and at 74° only eleven days. Radishes vary with the 

 temperature from six to twelve days. Thus the average temperature of any 

 country, other things being equal, may be inferred with considerable accuracy 

 from the periods of vegetation ; for, in looking over my long list of recorded 

 experiments, I find a great degree of uniformity in the process of germination, 

 in ordinary circumstances. 



After various experiments, I have succeeded in ridding my peas of the bug 

 (-Sruchus pisi). Immediately after gathering the seed, I subject them to the 

 action of boiling water one minute ; by this means I destroy the little grubs, 

 or larvae, which at this time are just below the integuments of the pea, without 

 destroying the vitality of the seeds. If the peas remain in the boiling water 

 four minutes, most of them will be killed, but not all ; of about forty peas 

 thus treated last year, three vegetated, and are now growing. The corcle, T 

 find, is more tenacious of life than the cotyledons. {Dr. J, T. Plummer ; in 

 iSilIiman's Journal, Jan. 1841, p. 198.) 



Growth of Fig Branches without Roots. — In the autumn of 1839, I made a 

 basket for an orchideous plant from the branch of a fig tree ; which, when filled 

 with suitable materials and hung up, soon commenced growing, producing 

 leaves of a moderate size, and also roots, which penetrated the fibrous mass 

 filling the basket. As these produced a curious appearance, and afforded 

 agreeable shade to the roots of the plant cultivated in the basket, I allowed 

 them to remain, and during the growing season shoots 2 or 3 inches long 

 were formed, and ripened. This has been the case annually, and the 

 young shoots of the present season are bearing fruit ; which is, I think, a 

 curious and very striking instance of the very different treatment plants may 

 endure, and still be able to complete every purpose for which they Avere 



