208 ESSENTIALS OE BOTANY 



genus. The number of species in a genus varies widely, — 

 the Kentucky Coffee-tree genus contains only one species, 

 while the Golden-rod genus comprises more than forty 

 species in the northeastern United States alone. 



257. Hybrids. ■ — If the pollen of a plant of one species 

 is placed on tlae stigma of a plant of the same genus but a 

 different species, no fertilization will usually occur. In 

 a large number of cases, however, ovules will be fertilized 

 and good seed be produced. This process is called hyhridi- 

 zation, and any plant grown from such seed is a hylrid.^ 

 Many hybrid oaks and violets have been found to occur 

 in a state of nature, and hybrid forms of wheat, orchids, 

 grapes, and other cultivated plants are produced by plant 

 breeders at will (Chapter xxix). 



258. Varieties. — Oftentimes it is desirable to describe 

 and give names to subdivisions of species. All the culti- 

 vated kinds of apple are reckoned as belonging to one 

 species, but it is convenient to designate such varieties as 

 the Baldwin, the Bellflower, the Rambo, the Gravenstein, 

 the Northern Spy, and so on. 



259. Family. — Genera which resemble each other some- 

 what closely are classed together in one family. The 

 particular genera mentioned in Sect. 255, together with a 

 large number of others, combine to make up the Buttercup 

 family. In determining the classification of plants most 

 points of structure are important, but (in the case of seed- 

 plants) the characteristics of the flower and fruit outrank 

 others because they are more constant, since they vary 

 less rapidly than the characteristics of roots, stems, and 

 leaves do under changed conditions of soil, climate, or other 

 surrounding circumstances. Mere size or habit of growth 



1 See L. H. Bailey's Plant Breeding, Tbe jMaciuillan Company, New York. 



