336 
LOCK : STUDIES IN PLANT BREEDING 
of fertility, is shown to be a foreshadowing of the distinction 
between Mendelian and unisexual crossing ; and forms 
which differ only by such characters as obey Mendel’s Law 
when crossed are fertile together. Forms, on the other 
hand, which differ by true specific distinctions exhibit 
infertility which increases with the number of such differ¬ 
ences up to complete sterility. 
Correns (22) has criticized these views of de Vries. He 
finds that de Vries’ supposition—Mendel’s Law holds good 
for varietal characters, whereas species-characters on crossing 
yield constant hybrid-characters—-does not hold generally 
good. Correns has described cases in Zea Mays in which 
hybrids in respect of varietal characters give constant pro¬ 
geny. On the other hand, certain “ species-” characters, 
for example, some of those which Bateson has examined in 
the case of poultry, have been shown to follow Mendel’s 
Law. 
In opposition to de Vries’ view of the existence of an 
unpaired character in the case of unisexual- (species-) 
hybrids, Correns believes that the rudiment of a correspond¬ 
ing character exists in the other parent form ; since the 
‘^progressive ” character does not really pass over unmodified 
in the unisexual cross, but is reduced to half its former 
value. Correns believes that a progressive mutation takes 
place by the modification of a pangen already existing, not 
by the formation of a completely new one. He would, 
therefore, speak of a pair of “ Anlagen ” in this case also. 
De Vries regards a “ retrogressive ” mutation as taking 
place simply by a process of becoming latent (i.e., inactive), 
of a pangen. But Mendelian hybrids not infrequently show 
characters intermediate between those of their parents, as 
Correns has clearly shown ; hence in this case the “ re¬ 
cessive ” allelomorph has a distinct effect, and is not entirely 
latent. Here again Correns would speak of a pair of “ An¬ 
lagen.” So also Bateson, who uses the term “pair of 
allelomorphs.” 
