that it had the smell of common Tansy, and ultimately 

 proved it to be that plant, which had been so changed by 

 growing in the dark. Indeed it was recollected, that 

 some soil had been taken into the drain from a neighbour- 

 ing garden, some time before it was found so altered. 



It has been ascertained, by experiment, that the green 

 colour of vegetables may be produced by the light of a 

 lamp, in the absence of the more perfect light of the sun; 

 as discovered by the Abbe Tessier. 



Leaves give out moisture by their under surface, in pro- 

 portion to the intensity of light, and not of heat; so that 

 there is scarcely any evaporation during the night. The 

 water which exhales from vegetables is not pure, but 

 serves as the vehicle of the aroma ; it is equal to the third 

 part of their weight every twenty-four hours, in healthy 

 plants. 



Leaves also expose the sap which they receive from the 

 wood, to the action of the air, and return it again to the 

 bark by its fibres or vessels. They also serve to nourish 

 and prepare the buds of the future shoots, which are always 

 formed at the base of the leaf stalk, and to shade them, as 

 well as the fruit, from the too powerful heat of the sun. 

 Hence it is, that in tropical countries the tree is never 

 divested of the leaf. 



Water is the only aliment which the root draws from the 

 earth ; and a plant can live and propagate itself, without 

 any other assistance than the contact of water and air ; as 

 may be seen every day, in the Hyacinth, and other bulbous 

 plants, which adorn our mantlepieces, as well as gramine- 

 ous, or grassy plants, such as wheat, &c. raised in saucers 

 or bottles, containing mere water. 



In vegetables, hydrogen is the principle which fixes 

 itself, while oxygen gas (the other constituent part of 

 water) makes its escape. 



But although pure water is more proper for vegetation, 

 than water charged with salts, yet water may be disposed 

 in a more favourable manner to the developement of vege- 

 tables, by charging it with the remains of vegetable and 

 animal decomposition : the plant then receives juices al- 

 ready assimilated to its nature. Independent of those 

 juices already formed, the nitrogen gas (which has already 

 been mentioned, as constituting one of the nutritive prin- 

 ciples of plants) is abundantly afforded by the alteration 

 of vegetables and animals, and must facilitate their devel- 

 opement. 



Although it has been proved, by various experiments, 

 that pure water is sufficient to the support of plants, we 

 must not, therefore, consider the earth as of no use ; it 

 imbibes and retains water ; it is the reservoir destined by 

 nature to preserve the elementary juice which the plant 

 continually requires ; and to furnish that fluid in propor- 

 tion to its wants, without exposing it to the equally fatal 

 alternatives of being either inundated, or dried up. 



The nature of the soil must be varied accordingly as 

 the plant requires a more or less considerable quantity of 

 water, in a given time ; and accordingly as its roots ex- 

 tend to a greater or less distance. Every kind of earth 

 is not suitable for every plant ; and, consequently, a slip 

 cannot be grafted, indifferently, upon every species. 



A proper soil, is one which affords a sufficiently firm 

 support to prevent the plant from being shaken ; which 

 permits the roots to extend themselves to a distance with 

 ease; which becomes impregnated with humidity, and 

 retains the water sufficiently, that the plant may not be 

 without it when wanted. 



To answer these several conditions, it is necessary to 

 make a proper mixture of the primitive earths, for none 

 of them in particular possesses them. 



Siliceous (white sand) and Calcareous (limy) rnay be 

 considered as hot and drying ; the Argillaceous (clayey), 

 moist and cold ; and the Magnesium, (a primitive earth, 

 having for its base a metallic substance, called Magnesium, 

 generally found in combination with other substances,) as 

 possessing intermediate properties. Each, in particular, 

 has its faults, which render it unfit for culture : clay ab- 

 sorbs water, but does not communicate it; calcareous 

 earth receives and gives it out quickly ; but the properties 

 of these earths are so happily opposed, that they correct 

 each other by mixture. Accordingly we find, that, by add- 

 ing lime to an argillaceous earth, this last is divided ; and 

 the drying property of the lime is mitigated, at the same 

 time that the stiffness of the clay is diminished. 



Saline substances have been supposed of importance in 

 vegetation by some, but they do not appear essential to 

 the growth of any sort of plant except the Marine ; such 

 matters may, however, be of use to vegetation, though not 

 essential to it. That of common salt may operate upon 

 plants as it does upon the human body, by assisting to 

 digest the food, without furnishing nutriment itself. 



It is upon this principle, I presume, that common table 



