226 PRACTICAL COURSE IN BOTANY 



— prove that the offspring from crossing different plants of 

 the same kind is usually stronger and more productive than 

 that from self-fertilized ones ; and if the parent stocks are 

 grown in different places and under different conditions, the 

 offspring is more vigorous than that from the same kind of 

 plants grown under like conditions. For instance, plants 

 from crossed seeds of morning-glory vines growing near each 

 other exceeded in height those from self-fertilized seeds as 

 100 : 76 ; while the offspring of plants growing under different 

 conditions exceeded those of the other cross, in height, as 

 100 : 78 ; in number of pods, as 100 : 57, and in weight of 

 pods, as 100 : 51. Knowledge of this kind, when applied to 

 the raising of fruits and grains for market, is of incalculable 

 value to gardeners and farmers, and also to the amateur who 

 raises fruits or flowers for pleasure. 



256. Hybridization is the crossing of two plants of differ- 

 ent species or of widely separated varieties of the same species. 

 The resulting offspring is a hybrid. Hybridization can take 

 place only within certain limits. If the species are too unlike, 

 the pollen will either not take effect at all, or the resulting 

 offspring will be too weak and spindling to live ; or if they 

 survive, will not be able to set seed (Exp. 79). 



257. Effects of hybridization. — The most important prac- 

 tical uses of hybridizing are: (1) it " breaks the type " by 

 causing plants to vary, and thus gives the breeder a fresh 

 starting point for a new strain; and (2) when the parent 

 species are not too unlike, it accentuates the good effects of 

 crossing, and sometimes gives rise to offspring greatly sur- 

 passing either parent in size and vigor. In regard to varia- 

 bility it may act in three ways: (1) the hybrid may wholly 

 resemble one parent or the other, in which case there is, of 

 course, no variation ; (2) it may resemble one parent more 

 than the other ; or (3) it may show a blending of the charac- 

 ters of the two, as when a cross between a red poppy and a 

 white gives rise to a light pink, or a mixed red and white 

 variety. In the first two cases, the characters of the parent 



