WHITE— STUDIES OF INHERITANCE IN PISUM. 



545 



apparently secured all three classes in some cases in F^, i. e., tall, 

 dwarfs and half dwarfs. Lock (54) secured only tails and half 

 dwarfs, but the half dwarfs were of two types in some cases — those 

 with a relatively small number of long internodes and those with a 

 relatively large number of short internodes. The tails were made 

 up of a large number of long internodes. 



Tails X dwarfs in F^ give tails, often considerably taller than the 

 tall parent. In F^, tails and dwarfs appear in a ratio approximating 

 3:1. Lock (54), Hurst (42), Bateson and others have confirmed 

 Mendel's original results. Mendel obtained in Fo from a total of 

 1,064 plants, 787 tails and 277 dwarfs or a ratio of 2.84: i. Of 100 

 Fo tails, 28 bred true in F3, while yz F^ tails gave both tall and 

 dwarf offspring, approximating a ratio of 2:1. The dwarfs bred 

 true. Two more generations of this cross were grown by iNIendel 

 without securing exceptional results. 



Half dwarfs X half dwarfs gives in F^ in some cases only half 

 dwarfs, or tails due to heterozygosis (i, 54) which give rise in Fr, 

 and succeeding generations to half dwarfs. In other cases (49), 

 involving a different set of varieties, the F^ is extremely tall, while 

 the Fo generation consists of tails, two types of half dwarfs and 

 dwarfs in a ratio approximating 9:3:3:1. Keeble and Pellew 

 crossed two half dwarf varieties differing for the most part in only 

 three characters — length and number of internodes and in diameter 

 of stem. Thick stems, short internodes in large number (I.) X thin 

 stems, long internodes in small number (II.) gave in F^ plants with 

 thick stems, long internodes in large number. In Fo, 5 Fj plants 

 gave rise to 192 progeny of 4 types as follows: 



The dwarfs in this particular case all had thin stems and short 

 internodes. 



Half dwarfs X dwarfs in F^ in some cases give intermediates 

 (i, 3) ; in other cases half dwarf height is dominant. In a case of 

 the latter type, Tschermak (81) obtained half dwarfs and dwarfs 

 in Fo and the dwarfs remained constant in F,. 



