174 INTRODUCTION TO BOTANY 
165. Unit characters.!. Much more definiteness has recently 
been given to the discussion of questions relating to plant 
breeding by the introduction of the idea of writ characters. 
Every species or variety of animal or plant is considered by 
many authorities to be composed of a set of unit characters, 
or simple features by which it is distinguished from other 
species or varieties. Just what this statement means will ap- 
pear more clearly if some of the unit characters which belong 
to different varieties of a familiar species of plant are set 
down. In the case of timothy, our most important grass for 
haymaking, twenty-eight opposing character pairs have been 
noted. Some of these are 
Heads 
Long or short 
Continuous or interrupted 
Large-seeded or sinall-seeded 
(and 8 others) 
Leaves 
Long or short 
(and 4 others) 
Stems 
Tall or short 
Many or few branches from the base of the stem 
(and 4 others) 
Nodes 
Near together or widely separated 
(and 2 others) 
Habit characters 
Inclined to blow down or remaining erect 
Rusting readily or rust-resistant 
Early or late maturing 
Careful breeding would probably soon give a variety with 
any one of these twenty-eight characters strongly marked, 
and several of them could be combined in a single variety if 
desired. 
1 See the valuable summary of this subject, given by Professor Herbert J. 
Webber in his address before the American Breeders’ Association, Science, 
April 19, 1912, 
