PLANT BREEDING 69 



the other hand, plants which show a great amount of 

 variation between the individuals growing together, 

 are generally suspected of being the results of cross- 

 breeding, or hybrids, as they are called, because by 

 experiment it has been shown that the results of cross- 

 breeding from slightly different stocks is to induce a 

 great amount of variability in the offspring. 



Now, in the vegetation which is untouched by man 

 indeed in the past vegetation that had been flourishing 

 before ever man appeared there have been innumerable 

 opportunities for cross-breeding, both between closely 

 allied species and those remote in characters, because 

 most flowers are open to the face of heaven, and there 

 are the wind and innumerable insects to act as distri- 

 buting agents for the pollen. Many flowers are so 

 wonderfully adapted that the chance of unexpected 

 pollen reaching the stigmas is very slight, while in all 

 cases the mixture of two very remote races is prevented 

 by the inability of pollen to develop in alien tissue. 

 Yet that still leaves enormous possibilities for the for- 

 mation of natural hybrids. A pretty example of natural 

 hybrids with a good deal of variation is the case of 

 Primroses and Cowslips, with the varieties of the hybrid 

 Oxlips which have resulted from their interbreeding. 



Scientists have not yet decided how much the vari- 

 ability in what appear as pure races is due to the im- 

 mediate environment of the individual, and how much is 

 the effect of interbreeding in the distant past of the stock, 

 but, be that as it may, the fact remains that there is 

 this variability, and that it is in the highest degree 

 important to the farmer and fruit grower. Fruit or 

 flower growers, for instance, cross the pollen from one 

 plant on to the stigma of another that has some quality 

 they want to breed. From the great variety of offspring 

 in a successful cross they select the ones that approxi^ 



