No. 464] STUDIES ON PLANT CELL—VH. 573 
of others, who have confirmed his conclusions, is the discovery 
in a number of animals and plants that the germ cells of the 
hybrid may be pure with respect to certain characters of the 
parents which are crossed. This principle is not without excep- 
tions where the conditions are apparently complicated by unusual 
factors but the phenomenon when present is so striking as to 
command immediate attention and call for an explanation on a 
cytological basis. The purity of the germ cells of hybrids means 
in the words of Castle that **the hybrid, whatever its own char- 
acter, produces ripe germ cells which bear only the pure char- 
acters of one parent or the other." Thus if two forms A and B 
are crossed the hybrid will have embodied in itself the characters 
AB, one of which however may lie latent, 7. ¢., may not be visi- 
ble in the hybrid. Such a latent character when present is 
termed recessive while the prominent character is termed domi- 
nant. Ina simple case some of the offspring of the hybrid AB 
will be found to have the character of A alone, some of them of 
B alone, and some of them will again have the mixed characters 
AB. If experiments are carried out on an extensive scale the 
proportions of these offspring from the hybrid may exhibit the 
remarkable fact that there are about twice as many forms of AB 
as either A or B, z. e, the proportions of A's, AB's, and B's are 
in the ratio of 1:2:1. Furthermore the offspring of A when 
bred among themselves remain absolutely true producing a suc- 
cession of pure forms all A's and the same results follow when 
the offspring of B are closely bred. But when forms with the 
mixed characters AB are bred with one another their offspring 
break up as before into three types A, AB, and B in numerical 
proportions expressed by the same ratio 1:2:1. The history 
is simply told in the following diagram where the number of off- 
spring is assumed to be 4. 
Acei E IDAs. oss: 64 A 
( 2A.....- BA. ae 32 A 
Form A ( 4A: +... UM 
Hybrid AB< 2AB« 4 AB4 SAB! ı6AB 



8 
4B... 16 B 
roma p | 2B....-. l ERI VS 32 B 
1B e 4B... 16 B. ose 64 B 
