be self-pollinated if at all. He cross-pollinated others. As 

 a result he found that those that were cross-pollinated set 

 more seed, the seed weighed more, and the plants coming 

 from them were more thrifty, on the average, than those 

 produced by self-pollinated flowers. Other observers have 

 found the same thing to be true. There is thus some 

 advantage in crossing plants and animals, and the devices 

 that we have seen that aid in crossing are expressions of 

 this advantage. Some plants, however, seem to do quite 

 as well with self-fertilization as with cross-fertilization. 



6. Why is Cross-Fertilization Advantageous? This 

 question is not easy to answer. We have not yet got to 

 the place where the biologist can say just what is gained 

 by mixing different strains in this way. It seems in some 

 way related to this mingling of protoplasms, nuclei, 

 and chromosomes, which have different history and 

 composition. It is possible that new and different 

 protoplasm coming in froin the outside sperm is more 

 stimulative to the egg than that from the same parent. It 

 seems also that there is more chance for variety in the 

 offspring when two different strains are mixed than when 

 both cells are of the same strain. 



From this last mentioned fact, whether this can be 

 regarded as an advantage to the plant or animal species, 

 we can readily see how it may be of advantage to man. 

 By crossing different apples or peaches or daisies, or 

 cattle and hogs, we get new strains, sometimes of no 

 values, sometimes a kind of mingling of character of both 

 parents in different degrees, and sometimes a result 

 decidedly more perfect for our uses than either of the 

 parents. Very much of the improvement in most of our 

 cultivated animals and plants has been possible because 

 of this mixing of breeds, together with the selection of 

 what suits us best out of the results. 



7. The Limits of the Crossing. We have seen that in 

 mingling gametes there seems to be some advantage in 

 having the gametes different, as in male and female 

 parents. Where nature lays so much emphasis we have 

 come to feel there must be something worth while. There 

 is, however, a limit to the difference that is possible in 

 gametes and in parents. If we select parents of different 

 varieties, or particularly of different species, the offspring 

 are quite certain to be different from either and often are 

 not so good as either. 



The following rules may help the reader appreciate this: 



a. The more different the parents are the less likely 

 their gametes are to unite. We may cross different 

 species of lilies or different species of roses, but we 

 cannot cross lilies with roses. 



b. If fertilization succeeds, the more different the 

 parents are, the more likely is the offspring to be 

 imperfect. For example, we can cross the different 

 varieties of horses readily enough. We can also 

 cross the horse with the ass, and the result is the 

 mule. The mule has qualities that make it a better 

 animal for some human uses than either the horse 

 or the ass. The mule, however, is entirely unable 



; to breed. It cannot breed with either parent or with 



other miiles. Its gametes seem to be imperfect. 



The horse and ass are of different, but related, 



species. The individual plants or animals which 



result from crossing different species are called 



hybrids. Hybrids are not all sterile, as is the mule. 



In the human race the different varieties may cross. It 



seems that there may be some gain in the crossing of 



peoples nearly akin, as the English, German, French, etc., 



who are all branches of the Caucasian stock. The mixture 



of these different, but kindred, types often produces 



valuable results. There is, however, considerable evidence 



for the view that crossing the different races, as negroes 



with Indians, and negroes with whites, gives offspring 

 more of the nature of hybrids; and while they are not 

 necessarily infertile, they do not seem to have the vigor 

 of the original stocks. 

 FINALE. 



