UNITED STATES DEPARTMENT OF AGRICULTURE 
s%J^*^j , u 
\ BULLETIN No. 869 
Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 
Washington, D. C. 
PROFESSIONAL PAPER 
September 30, 1920 
THE INHERITANCE OF THE LENGTH OF INTER- 
NODE IN THE RACHIS OF THE BARLEY SPIKE. 
By H. K. Hayes, Head of Section of Plant Breeding, Division of Agronomy and Farm 
Management, College of Agriculture, University of Minnesota, and Harry V. Har- 
i lan, Agronomist in Charge of Barley Investigations, Office of Cereal Investigations. 
CONTENTS. 
Page. | 
Scope of the experiments 1 
Historical review 1 
Pure-line varieties used in these studies 3 
Reliability of experimental methods 4 
Effects of environment and varying sources 
of seed on density 5 
Purity of parental forms 5 
Page. 
Inheritance of length of internodes in crosses 
between pure lines : 9 
Summary of results 20 
Discussion of results 21 
Conclusions 24 
Literature cited 25 
SCOPE OF THE EXPERIMENTS. 
In 1915 a series of studies on the inheritance of the length of 
internode in the rachis of the barley spike was begun in cooperation 
with the Minnesota Agricultural Experiment Station. Internode 
length is a particularly favorable character for such investigations, 
as a large number of varieties furnish many gradations in internode 
length and in a pure line the average internode length of the rachis 
varies comparatively little from year to year. 
The project was undertaken for two main reasons, (1) as a study 
of inheritance in an unusually favorable size character and (2) as a 
contribution to the question of the taxonomic value of the length of 
internode of the rachis. 
HISTORICAL REVIEW. 
The length of internode is frequently referred to as density, and 
both terms are used in this bulletin. As far back as Linnaeus, species 
were differentiated by this character. With fertility, it has been, 
consciously or unconsciously, one of the main bases of classification 
182694°— 20— Bull. 869 1 
