INFLUENCE OF EXTEllNAL AUENTS ON VEUETATION. 



lias not nature given corUiin arums the odor of a leg of mutton, that has hung too 

 King? lias she not given to tlie IJuddloa the color and the odor of the stamens of the 

 palTi'in ? Has she not? But you must have proofs! Monsieur Vje'.ievos nothing 

 without proofs. In good sooth, my friend, I must tell you the truth, you become quite 

 unsociable; there is no such thing as holding a conversation with you, none of the 

 ingenuousness of friendship; everything assumes the air of a thcorum, you must have 

 proof of everything. It Avill not be long before you will require proof that the sun 

 shines, or that it rains. And truly, I don't know how we shall furnish you with it, 

 &e., &c. 



This nonsense uttered with the utmost confidence by five or six men, and all directed 

 against this poor fellow, whom they constantly accused of incredulity and Voltairanism, 

 whom they style a skeptic, strong minded, or M. Arouet, ended by completely turning 

 his brain. 



INFLUENCE OF EXTERNAL AGENTS ON VEGETATION. 



FROM darby's botany OF THE SOUTHERN STATES. 



The agents which exercise a decided influence on vegetation are li^M, heal, water, and 

 earih. 



The concurrent influence of all these agents, in a greater or less degree, is absolutely 

 required for the perfection of vegetable products; and according as some of them exist in 

 excess, or in diminished quantity, is the functional operation of the vegetable organs 

 injured or destroyed. Dificrent plants require these agents in very difi'erent degrees, and 

 hence the distribution of plants over tha face of the globe; some flijurishing near the 

 snow line of the mountains, or near the limits of perpetual snow, north or south, while 

 others can exist only under the influence of tropical heat. Some grow amidst the sandy 

 deserts, others only immersed in water. Some grow in the caverns of the earth while 

 others must have the direct rays of the sun. Some require a rich soil, others grow sus- 

 pended in the air. From this adaptation of vegetation to every variety of influence, the 

 earth is covered with verdure ; from the perpetual snows of the mountains or the arctics 

 to the equator, each position giving existence to its appropriate flora. 



Light. — The most obvious effect of light on vegetation is the production of colors, and 

 this it effects by decomposing carbonic acid, and depositing the carbonaceous matter. In 

 most cases, certainly, light is absolutely necessary for the deposition of the green color- 

 ing matter, since most plants become perfectly colorless by growing in situations in which 

 they are deprived of light. There are cases, however, in which plants deposit the green 

 chromule, when excluded from the light. Green vegetables have been found in cares of 

 the earth, fr 'm which the light of day was excluded, and we have seen the cotyledons of 

 the Mustard and the Impatiens balsaraiua green, when the seeds have germinated within 

 the perfectly closed pericarp ; and I have now before me a large onion in which several 

 of the central layers are as green as the leaves, while the parts above and around them 

 are perfectly white. That these are exceptions to a general rule is manifest from in- 

 numerable examples to the contrary, constantly occurring within the observation of every 

 one. If a board lies upon the grass for a short time, the grass becomes blanched ; plants 

 growing in a dark cellar are colorless ; the interior of the cabbage is white, while the 

 other leaves are green, and if these are ronioved, those that are exposed soon become 

 green. Plants, which in their natural situation are white, by accidental exposure become 

 green ; the side of a potato from which the soil has been by chance removed, soon 



