150 HEAT. 



rican Marigold, Tagetes Patula^ and Sunflower, Hilianthus An- 

 nuuSf but Mr. Trimmer, in an article in the 2d vol. of " Pax 

 ton's Magazine of Botany," p. 193, observes that he had ob- 

 served it in many other flowers. ' 



220. The cause is supposed to be electrical, as the flashes 

 are more brilliant, when the atmosphere is most highly charged 

 with electricity. In walking in my garden, says Mr. Trim- 

 mer, in which was a considerable quantity of Nasturtium in 

 bloom, not at all thinking of the flashing of plants, I was 

 struck with the very vivid flashes that proceeded from them ; the 

 scintillations were the most brilliant that I had ever observed, 

 at the same time the cky was overcast with a thunder cloud; 

 and he further remarks, that he always found them most bril- 

 liant under such circumstances. 



Section 2. Heat. 



221. Heat is the most obviously necessary, of any external 

 agent, to the existence and growth of vegetables ; without a 

 considerable degree of it, no vegetation takes place. We ob- 

 serve amid the colds of winter, vegetable life is suspended, 

 and as the warmth of spring comes on, vegetation commences, 

 and as the heat increases, plants become more vigorous, in 

 the same proportion. 



222. The beautiful arrangement in the vegetable economy, 

 for the adaptation of vegetables, to this season of repose, can 

 but aflford matter for the most agreeable contemplation. In 

 equatorial regions, where heat is constant, a great proportion 

 of the vegetables, are of a peculiar organization, not yielding 

 their leaves, not covered with bark, and producing no cover- 

 ings to the buds ; while in higher latitudes we find our forest 

 trees expressly adapted to a season of repose, or a kind of 

 hybernation. The leaves at the approach of summer come 

 forth in immense profusion, perform with energy their func- 

 tions, during the heat of summer, and at the approach of au- 

 tumn, disengage themselves, by their own depositions, from the 

 parent stock. We find also our forest trees, covered with a 

 thick bark, composed of materials possessing the least power 

 for conducting caloric ; and the buds, the rudiments for 

 the perfection of which the succeeding year's energies are to 

 be devoted, enclosed in scales, nicely fitted for the protection 

 and preservation of their important contents. The equatorial 

 regions are emphatically the regions of monocotyledons, des- 

 titute of bark, and always in verdure. The temperate regions, 

 with the year distinctly marked by the four seasons, is as 



