PLANT BREEDING 347 



interpretations need not bother us. Suffice it to say that most plant 

 breeders have accepted the explanation that the recessive character is 

 simply the lack or absence of the character in question, while the dom- 

 inant character is its presence. This is simply a slightly different in- 

 terpretation of the same facts and simplifies some of the more complex 

 results of crossing. Instead of 50 per cent, of the germ cells bearing 

 the flint character and 50 per cent, bearing the sweet character when 

 sweet corn is crossed with flint corn, one should think of all of the 

 germ cells bearing the ability to produce the wrinkled sweet corn seeds, 

 but that 50 per cent, of them contain in addition the presence of a flint 

 or starch producing character. In other words, the " starchy " char- 

 acter is superimposed upon the " sweet " character. The dominant and 

 recessive characters in such a cross, then, are simply the presence and 

 absence of the starchy character. 



When several character pairs differentiate the two parent plants in 

 a cross, all possible recombinations are formed, the relative frequency 

 with which the combinations occur being simply the algebraic product 

 of as many of the simple ratios as there are character pairs. 



The importance of these Mendelian facts to the commercial plant 

 breeder is great. In crossing plants differing in several simple char- 

 acters that segregate after hybridization he may rest assured of two 

 things. First, that with a sufficient number of progeny in the second 

 hybrid generation, every possible recombination of the characters pres- 

 ent will be represented by at least one 'pure specimen. Second, that 

 these pure specimens when selfed, or pollinated with their own pollen, 

 will breed true. It should be remembered, however, that one may have 

 to self a number of plants to get the combination desired with all 

 characters pure, for if any dominant characters are concerned, their 

 purity can be ascertained only by breeding for another generation. 

 As an illustration we may take the snap dragon, Antirrhinum. There 

 is a long series of colors that segregate. There is also a type called the 

 " Delilah," where the tube of the corolla is uncolored. Starting with 

 this form in only one color, the whole color series of Delilah forms may 

 be reproduced by crossing with the self colored strains. Or, one may 

 combine the dwarf habit of growth of the Dwarf Champion tomato, 

 with any of the various colors and shapes now on the market which 

 have the ordinary tall habit of growth. Sometimes a very simple re- 

 combination is of very great commercial value. The so-called Havana 

 type of wrapper tobacco grown in the Connecticut Eiver valley has 

 large leaves and a short stocky habit of growth. It produces from 

 nineteen to twenty-one leaves. There is another type grown under 

 cheese cloth shade which has a tall habit of growth with about twenty- 

 six smaller leaves. The tall slender habit of growth makes it an undesir- 

 able type to grow in open fields where it is apt to be blown down. Mr. 



