238 A TEXTBOOK OF GENERAL BOTANY 
dominant. Thus, the fact that a character is dominant in one 
species does not necessarily imply that it is dominant in other 
species. Such facts can be determined only by observation. 
On examining Fig. 233 we find that the factors for tallness 
and dwarfness are inherited in exactly the same way as the fac- 
tors for color in four-o’clock plants. When a pure strain of tall 
peas is crossed with a dwarf one, the plants of the first hybrid 
generation contain a factor for tallness and also a factor for 
dwarfness, even though the factor for dwarfness is recessive. 
These plants, if self-pollinated, will produce three kinds of plants, _ 
even though, on superficial examination, there would appear to 
be only two. The three kinds are produced in a ratio of one 
which has two factors for tallness and none for dwarfness, and 
so can produce only tall offspring ; two which contain both the 
factor for tallness and the factor for dwarfness, and so can pro- 
duce both tall and dwarf offspring; and one which contains two 
factors for dwarfness and none for tallness, and so can produce 
only dwarf offspring. The plants which contain both the factor 
for tallness and the factor for dwarfness will be like their hybrid 
parents in hereditary height factors, and so will naturally give 
rise to the same kinds of plants as did their parents, and in 
the same proportion. 
In writing the abbreviations of characters it 1s very conven- 
ient as well as customary to represent the dominant character 
by a capital letter, as 7 for tallness, and the recessive character 
by the same letter not written as a capital. Thus, when tall- 
ness is dominant over dwarfness, dwarfness may be indicated by ¢. 
Inheritance of two pairs of characters. When we observe 
any organism we see that it is a morphological and physiolog- 
ical unit. From the standpoint of inheritance it is, however, 
made up of a number of hereditary units or characters, which 
most often appear to be inherited independently of each other. 
The examples of inheritance which we have considered demon- 
strate very clearly the segregation of characters and the purity 
of gametes, while the inheritance of height in peas is a good 
example of dominance. The independence of characters can be 
