10 APPLICATION OF PRINCIPLES OF HEREDITY TO BREEDING. 



pollen it follows that one-fourth of the progeny of the hybrid will be 

 pure reds. Similarly, the W ovules are offered both kinds of pollen, 

 and the chances are that half of these ovules, or about half, will be 

 fertilized by R pollen, the other half by W pollen. The latter half 

 being fertilized by pollen of their own kind result in pure white 

 individuals, which we may, for convenience, designate as WW indi- 

 viduals, thus indicating that both the ovules and the pollen which 

 gave rise to these individuals had the character W. The WW indi- 

 viduals also constitute one-fourth of the progeny of the hybrid. 

 The remaining half of the progeny result from the fertilization of 

 one kind of ovule by the opposite kind of pollen, thus giving hybrids 

 like the original hybrid, which we may designate by the formula R W. 



We thus see that the supposition that the hybrid produces two 

 kinds of pollen, one like the pollen of the red variety and the other 

 like that of the white, and tw^o kinds of ovules, differing in a similar 

 manner, fully explains the phenomena observed by the breeder of 

 the purple primrose. This hypothesis is further substantiated by 

 the following facts. If we apply the pollen of the hybrid to the 

 stigmas of the red variety, half the progeny thus obtained will be 

 red and half purple. This is easily understood if the hybrid pro- 

 duces two kinds of pollen in equal quantities. All the ovules of the 

 red variety have the character R. If half the pollen of the hybrid 

 carries R, then half the progeny will be RR, or pure red. If the 

 other half of the pollen carries W, then the other half of the progeny 

 will be of the type R W. That the hybrid produces two kinds of 

 ovules is shown also by the fact that if we apply pollen of the red 

 variety to the stigmas of the hybrid, half the resulting progeny will 

 be red and half purple. 



We may accept the hypothesis, therefore, that a hybrid plant 

 whose parents differ in respect to a single character pair produces 

 two kinds of ovules and two kinds of pollen, one kind being like 

 those of one of its parents, the other kind like those of its other 

 parent. 



If a hybrid which has in its cells two characters which are natur- 

 ally the opposite of each other can not produce ovules and pollen 

 with both of these characters in the same ovule or pollen grain, then 

 it follows that these two opposite characters can not be transmitted 

 together. They remain together in the cells of the hybrid well 

 enough, but they fall apart somewhere in the process of producing 

 reproductive cells. Let us now inquire how this segregation of the 

 members of a pair of opposite characters into different ovules and 

 different pollen grains, which takes place in hybrids, may occur. 

 In the cells of a plant we have, first, the outer covering, or cell wall. 

 Within is the nucleus, between which and the cell wall hes the 



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