214 ELEMENTS OF BOTANY. 



Coffee-tree genus contains only one species, wliile the Golden- 

 rod genus comprises more than forty species in the north- 

 eastern United States alone. 



258. Hyhrlds. — If the pollen of a plant of one species is 

 placed on the stigma of a plant of' the same genus but a 

 different species no fertilization will usually occur. In a 

 large number of cases, however, the pistil will be fertilized, 

 and the resulting seed will often produce a plant intermediate 

 between the two parent forms. This process is called hybri- 

 dization, and the resulting plant, a hybrid. Many hybrid 

 oaks have been found to occur in a state of nature, and hybrid 

 forms of grapes, orchids, and other cultivated plants are pro- 

 duced by horticulturists at will. 



259. Varieties. — Oftentimes it is desirable to. describe 

 and give names to sub-divisions 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 Eambo, the G-ravenstein, the Northern 

 Spy, and so on. Very commonly varieties do not, as horti- 

 culturists say, " come true," that is to say, the seeds of any 

 particular variety of apple not only are not sure to produce 

 that variety, but they are nearly sure to produce a great 

 number of widely different sorts. Varieties which will repro- 

 duce themselves from the seed, such as pop-corn, sweet corn, 

 flint-corn, and so on, are called races. 



Only long and careful study of plants themselves and of 

 the principles of classification will enable any one to decide 

 on the limits of the variety, species, or genus, that is, to deter- 

 mine what plants shall be included in a given group and what 

 ones shall be classed elsewhere. 



260. Order or Family. — Genera which resemble each 

 other somewhat closely, like those discussed in § 266, are 

 classed together in one order or family. The particular 

 genera above mentioned, togetlier with a large number of 



