Definitions. 3 



and producing the like forms of growth from their seeds. They are 

 subject to many variations, due to differences of soil, climate, and 

 other causes, and occasionally produce unusual forms in their leaves, 

 size and color of flowers, quality of fruit, or habits of growth, which 

 are called " sports." In other cases, hybrids will form by cross-fer- 

 tilization, the result being a tree that partakes of some of the char- 

 acteristics of both species. This is occasionally seen in the oaks and 

 the willows, but as a rule the species remain distinct. These devi- 

 ations from the normal type may be perpetuated by budding, graft- 

 ing, or layers, but when they bear fertile seeds, they do not produce 

 plants having like peculiarities, and tend to return to their original 

 forms. 



9. A Genus, rs usually a group of species having common resem- 

 blances in the structure of the flowers and fruit, and generally, in 

 their leaves and in the habit of growth, such as the pines, maples, 

 birches, etc. In some cases, however, a genus may include but one 

 species. They are sometimes divided into groups or sub-genera, 

 having some common resemblance, and occasionally these may be 

 further arranged into other groups, having common forms or prop- 

 erties. Where there are several species in a genus, they may be 

 generally grafted upon one another, but in other cases this can only 

 be done successfully within the group or sub-genus to which the 

 species belong. 



10. A Natural Order, in botany, is a class of trees or plants that 

 usually embraces several genera^having a common resemblance in 

 the structure of the seed and fruit and in manner of growth, differ- 

 ing from all others and constant within itself. These are again 

 sometimes divided into sub-orders, families, or groups, depending 

 upon a common resemblance, and instances occur in which a natural 

 order includes but a single genus. 



11. We have examples of natural orders in the Coniferce, embrac- 

 ing the pines, firs, spruces, cedars, junipers, etc., and in the Legum- 

 inosce, or bean-like fruited plants, which include, among trees, the 

 locusts, honey-locusts, acacias, Kentucky coffee-tree, and many 

 others. 



12. The description and classification of orders, genera, and 

 species among trees form a part of the province of botany, and will 

 not be attempted in this work. In mentioning the common names 



