608 Proceedings of the Royal Society of Edinburgh. [Sess. 
The results can therefore be tabulated as follows : — 
If D be the term for dominant, R that for recessive, DR that for impure 
dominant, P for the first crossing plants, and F^F" for the subsequent generations, 
we have 
D 
X 
R 
P 
tall 
|| d 
warf 
DR 
impure D 
F 1 
1 
D* 
DR 
Rt 
F 2 
1 : 
9 
: 1 
3 : 1 
Mendel established, therefore, that the qualities which make up a plant 
may be considered as unit-characters, and that the ones selected for study, 
whether single or coupled, were autonomous, that is, did not blend, and 
ultimately segregated into D : DR : R as 1:2:1. DR always gives D : R 
as 3:1. 
Thus in the tall-dwarf crossing, the plants in the subsequent generations 
were not intermediate in height between tallness and dwarfness, but 
segregated the parental selected unit-characters practically unaltered. 
To explain this, Mendel advanced his theory of gametic segregation. 
He supposed that his unit - characters of tallness and dwarfness were 
segregated pure in the gametes of the tall and the dwarf plant respectively. 
He stated his theory in the simplest case as follows. If A be the dominant 
character, a the recessive, and Aa the impure dominant (Mendel’s hybrid), 
then A + 2Aa>-\-a gives the terms in the series for the progeny of the 
impure dominants of two differentiating characters. (A +<x)(M + a) = M 2 
+ 2 A a + a 2 , i.e. M + 2M<x + (x; the square being neglected as not numerically 
efficient. In the same way, where more than one unit-character was used, 
the results of the crossing agreed with the algebraic expectation. 
I wish now to show that in human fertilisation we have a Mendelian 
action, but one, in my opinion, not in strict accordance with the views of 
Mendel. I must first define certain terms to be used. 
The ovum and the spermatozoon are termed gametes ; and, as I hold there 
are two kinds of each, I speak of a male sex gamete, a male non-sex gamete, 
a female sex gamete, and a female non-sex gamete. For the adult or 
developed plant or animal I use the term holophyte. The fertilised ovum 
is spoken of as the zygote ; and, as sex is considered to be determined as soon 
* Breeds true to tallness, and is an extracted dominant, 
t Breeds true to dwarfness, and is an extracted recessive. 
