A Report on Sterility in Irises 



by 

 liOuisie A. Cover, Ularjorie R. Swabey and A. B. Stout. 



INTRODUCTION 



Any grower of irises may readily observe that many of the fiowers 

 do not yield capsules and seeds. Since the structure of the flower is 

 adapted to insect pollination, some of this sterility may bo due to lack 

 of insect pollination. But the structure of the fiowers does not limit pol- 

 lination by insects from one flower to another flower of the same variety 

 or even from one side to another in the individual flower. Hence when 

 a variety is decidedly or even always fruitless wherever grown one 

 realizes that either insect pollination is entirely lacliing or that there 

 is some type of sterility present which is inherent and fundamental in 

 the nature of the variety and is independent of mere processes of pol- 

 lination. 



It is the inherent sterility (or sterilities) which the breeder of 

 irises will continually encounter. When the pollen is artificially sup- 

 plied and proper pollinations made under conditions favorable to seed 

 setting, the inherent sterilities operate to defeat the efforts that are 

 made to secure seed for breeding. 



An indication of the nature and the range of the inherent sterilities 

 in irises has been well presented by Miss Grace Sturtevant in an article 

 published in Bulletin No. 2 of the American Iris Society. In her survey 

 of experiences in breeding irises she finds four main groups of varieties 

 as follows: — 



1. Varieties that have proved fertile. 



2. Varieties that do not set seed but have fertile pollen. 



3. ' Varieties that set seed but the pollen is absent or sterile. 



4. Varieties that are sterile. 



Prom this it is evident that some varieties are fertile both as seed 

 and pollen parents, that some can function only as a seed or as a pollen 

 parent, and that others are sterile both as seed and as pollen parents. 

 Those who attempt to breed irises fro.m seed are certain to encounter 

 these sterilities and their efforts will in considerable measure, be facil- 

 itated by an understanding of what is possible and what is impossible in 

 seed breeding. To determine this more fully and for as many varieties 

 as possible was the aim of the investigation here reported. The work 

 was done at The New York Botanical Garden in cooperation with the 

 American Iris Society which provided the funds for the two scholarships 

 awarded for the study. The period of the work extended through May 

 and June 1925.* 



*The laboratory stiidie.s of the pollen were made by Miss Swabey and the 

 hand pollinations and field studies were made by Miss Cover. The research 

 was done under tho direction of Dr. A. B. Stout, of The New York Botanical 

 Garden who contributed most of the text, exclusive of the tables of this re- 



PO'"*- —Editors. 



