20 Principles of Plant Culture. 



different common names in this country alone, and yet, 

 in a given locality it is often known by only one name. 

 Its scientific name, however, Agropyrum repens (a-gro- 

 py'-rum re'-pens), is the same in all languages and 

 countries. Scientific names are usually Latin and con- 

 sist of two words. The first word is the name of the 

 genus to which the plant or animal belongs, and is called 

 the generic (ge-ner'-ic) name; the second word designates 

 the species, and is called the specific (spe-cif -ic) name. 

 For example, Purus mains (py'-rus ma'lus) is the scien- 

 tific name of common apple, Purus being the genus to 

 which the apple belongs, and mains designating which 

 species of the genus is meant. 



23. Crosses and Hybrids (hy'-brids). We have seen 

 that in sexual reproduction, a union of male and female 

 cells is almost always essential (17). When these cells 

 proceed from two individuals of different varieties (21, 

 436), the offspring is called a cross; when they proceed 

 from individuals of different species, it is called a hybrid. 

 Hybrids are possible only between closely-allied species 

 and are often incapable of reproduction, in which case 

 they are said to be sterile. The mule, which is a hybrid 

 between the horse and the ass, is a familar example of a 

 sterile hybrid. Sterile hybrids are not uncommon in 

 plants. A hybrid that is capable of reproduction is 

 called & fertile hybrid. 



Hybrids and crosses may resemble both parents about 

 equally or they may resemble one parent more than the 

 other. They sometimes differ materially from either 

 parent. The offspring of crosses and fertile hybrids is 

 generally variable in proportion as their parents were 



