=674b. Hybridization.=—Two different species are “crossed” where the egg-cell of one species is fertilized by the sperm of another species. The progeny resulting from such a cross is a _hybrid_. Hybrids sometimes resemble one parent, sometimes another, sometimes both. Where the parents differ only in respect to one character of an organ or structure, there is a regular law in respect to the progeny if they are self-fertilized. In the first generation all the individuals are alike and resemble one of the parents, and the special differential character of that parent is called the _dominant_ character. In the second generation 75% possess the dominant character, while 25% resemble the other original parent, and its differential character is called _recessive_. These are _pure_ recessives, since successive generations, if self-fertilized, are always recessive. Of the 75% which show the dominant character in the second generation, one-third (or 25% of the whole number) are pure dominants if self-fertilization is continued, while 50% are really “cross breds” like the first generation, and if self-fertilized split up again into approximately 25 dominants, 50 cross breds, and 25 recessives. This is what is called Mendel’s law. Where the original parents differ in respect to more than one character, the result is more complicated (see Mendel’s Principles of Heredity; also de Vries, Das Spaltungsgesetz der Bastarde, Ber. d. deutsch. bot. Gesell., 18, 83, 1900). =674c. Mutation.=—This term is applied to those variations which appear so suddenly that some of the progeny of two like individuals differ from all the others to a marked degree. Some of these mutations are so different as to be regarded as new species. Some of the primroses show mutations, and Œnothera gigas is a mutation from Œnothera lamarkiana (see de Vries, Die Mutationstheorie, Leipzig). =675.= TABLE SHOWING HOMOLOGIES OF SPOROPHYTE AND GAMETOPHYTE IN ANGIOSPERMS. TERMS CORRESPONDING TO THOSE USED IN PTERIDOPHYTES. COMMON TERMS. Sporophyte { = Higher plant. Spore-bearing part { = Stamens and { carpels. -------------------------------------------------------------------- { {Anther. Sporophyte {Microsporophyll = Stamen {Filament. { {Microsporangium = Pollen sac, { usually { two or four. -------------------------------------------------------------------- {Microspore at maturity = Pollen grain. { usually of 2 or 3 cells { {young male prothallium}