VEGETABLE PHYSIOLOGY. 67 



plants. An open soil, if not too light in its own nature, will 

 always produce plentiful crops. It readily receives the air, rains 

 and dews into its bosom, and at the same time gives the roots of 

 plants a free passage in quest of food. This is the true reason 

 why land well tilled is so remarkably fruitful. Water is thought, 

 by some, to be the food of vegetables, when in reality if is only 

 the vehicle of nourishment. Water is a heterogeneous fluid, and 

 is nowhere to be found in a pure state. It always contains a 

 solution of animal, vegetable or mineral substances. These 

 contribute to the nourishment of plants, and the element in which 

 they are minutely suspended, acts only as a vehicle, in guiding 

 them through the fine vessels of the vegetable body. As water 

 is necessary to the commencement of vegetation, so is it also 

 necessary to its progress. Plants will not continue to vegetate 

 unless their roots are supplied with water ; and if they are kept 

 long without it, the leaves will droop and become flaccid, and 

 assume a withered appearance. Now this is evidently owing to 

 the loss of water. For if the roots are -again well supplied with 

 water the weight of the plant is increased, and its freshness 

 restored. But many plants will grow, thrive and effect the 

 developement of all their parts, if the root is merely immersed in 

 water, though not fixed in the soil. Lilies, hyacinths and a 

 variety of plants and bulbous roots, may be so reared, and are 

 often to be met with so vegetating ; and many plants will also 

 vegetate though wholly immersed. Most of the marine plants 

 are of this description. It cannot be doubted, therefore, that 

 water serves as an important vehicle of vegetable aliment. 



The ingenious Dr. Priestley proves to a demonstration that the 

 putrid air arising from decaying substances, and the perspiration 

 of animals, is not only absorbed by vegetables, but also adds to 

 their increase. He contends that all plants, by their leaves, as 

 well as by their roots, imbibe these putrid vapors, which consti- 

 tute a part of their food. " During the summer months," says he, 

 " the atmosphere is full of putrid exhalations arising from the 

 steam of dunghills, the perspiration of animals and smoke. Every 

 shower brings down these oleaginous particles for the nourishment 

 of plants. It is pleasing to observe how the dissolution of one 



