INTRODUCTORY REMARKS. 9 



would not be more likely to effect this end in all this variety ; it 

 is doubtful, indeed, whether the useful plants would be so well 

 adapted to this state of things, as they generally require a more 

 favorable combination of circumstances. 



To secure this end, too, it is important that a host of plants 

 should have no natural attractions for animals, that they may grow 

 without molestation, and exert their influence upon the atmosphere 

 without interruption. 



This end is secured by the foliage of forests, which is chiefly 

 removed from all access of destructive agencies. 



It is a general fact, that animals multiply nearly in proportion to 

 the supply of food. If all vegetables were food for animals, the 

 entire action of a great multitude could not be employed, as it 

 now is, in purifying the atmosphere. 



In this grand respect, all plants are performing a work of the 

 highest utility. Unseen and silent, they renovate the very pabu- 

 lum of life. 



2. Another end of the vegetable kingdom is food for the ani- 

 mal. AH animal life is ultimately supported from the vegetable 

 world. But animal life abounds ; tens of thousands of smaller 

 animals, and especially of the insect tribe, must be dependent, as 

 well as the larger animals and man, upon vegetables. By their 

 foliage and seeds, the plants now considered as useless by many, 

 may give far more support in the article of food, than is com- 

 monly imagined. We know that many small birds derive much 

 food from seeds, as also a host of insects ; and yet we may be in 

 relative ignorance on this subject. Even the animals of the seas 

 must have no inconsiderable dependence upon vegetable substances 

 for their support. A great amount of decomposed vegetables must 

 be annually poured into the great reservoir by all the rivers. 



3. Plants enrich the soil, and fit it for the production of vege- 

 tables in greater quantity. This is true of vegetables generally, 

 when they live and die and decay on their place of growth. Cul- 

 tivation often exhausts land, because no adequate return is made 

 for the vegetable matter removed from the fields. The vegeta- 

 bles, often considered useless, will, by their decay, perform 

 another important service, in enriching the earth, and improving the 

 soil. It has long been remarked, that this effect follows, because 



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