UNITED STATES DEPARTMENT OF AGRICULTURE 



s^&t^su 



k 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- 

 lan, Agronomist in Charge of Barley Investigations, Office of Cereal Investigations. 



CONTENTS. 



Scope of the experiments 



Historical review 



Pure-line varieties used in these studies 



Reliability of experimental methods 



Effects of environment and varying sources 



of seed on density 



Purity of parental forms 



Page. 

 1 

 1 

 3 

 4 



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 Linnseus, 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 



