98 
V. //. Blackman. 
The first may be called the Pisum- type, because a number of 
the differentiating characters in Pea hybrids conform to this type, 
as Mendel showed. The second type is not known with certainty 
in nature; hybrids possessing a pair of characters of this kind 
would in the first generation exactly resemble the parent with the 
dominant character, and the second on later generations would be 
exactly like the first. In the case of the third type, hybrids with 
such characters would in the first generation show a character 
intermediate between those of the parents, the two characters would 
however be separated in the sexual cells, and the two kinds of 
gametes being produced in equal numbers there would arise, by self 
fertilisation, three classes of forms ; ( 1 ) 25 % pure forms with one 
character, ( 2 ) 25 % pure forms with the other character, ( 3 ) 50 % 
hybrid forms with the new intermediate character. The later 
generations would behave similarly and there would, as in Pea 
hybrids, be a rapid diminution in the proportion of hybrids in the 
offspring; as however there is no dominance of one character, the 
three classes of forms would always be clearly distinguishable. 
Examples of pairs of characters of this type are found in the hybrids 
between races of Zea Mays , so Correns terms this the Zea- type. 
In the fourth type the first generation of the hybrids would show a 
character intermediate between those of the parents and the later 
generations would be like the first; Hieracium hybrids exhibit a 
number of characters which conform to this rule so that Correns 
calls the type after this genus. 
Correns investigated with great care the behaviour, on crossing, 
of a large number of differentiating pairs of characters in thirteen 
constant races of Maize and found examples of all the types des¬ 
cribed above, except the second. Of the Pisum-type the best 
example was the chemical nature of the endosperm i.e. whether 
starchy or sugary. When a race with a starchy endosperm was 
crossed with a race with a sugary endosperm, the resulting hybrids 
had always starchy endosperm whichever way the cross was made ; 
in the second generation, after self-fertilisation, 25 % of the forms 
had sugary endosperm, the rest starchy, so that this pair of 
characters is clearly heterodynamic and schizogonous. To this 
category also belong pairs of characters in relation to the nature 
and colour of the glumes and also those relating to the colour of 
the endosperm and aleurone layer in the second and following 
generations (but not in the first). To the Zea -type were found to 
conform pairs of characters in relation to the form of the cells of 
