BULLETIN OF THE 



I 



No. 75 



Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief. 

 April 8, 1914. 



(PROFESSIONAL PAPER.) 



ALFALFA SEED PRODUCTION; POLLINATION 



STUDIES. 



By C. V. Piper, Agrostologist in Charge, and Morgan W. Evans, Koland McKeb, 

 and W. J. Morse, Scientific Assistants, Forage-Crop Investigations. 



INTRODUCTION. 



For a number of years past it has been a conspicuous fact that in 

 sections where alfalfa seed is grown commercially the yield varies 

 greatly from season to season. Particularly striking examples of 

 this variation in yield have occurred in the Milk River Valley of 

 Montana, where in some seasons yields of 10 to 12 bushels per acre 

 have been obtained, while in other years the crop was almost a 

 complete failure. It has been generally supposed that the visit of 

 certain insects to the flowers is absolutely necessary in order to 

 effect pollination. In accordance with this belief, some have held 

 that small crops of alfalfa seed were due to an unsatisfactory number 

 of pollinating insects, while others have suggested that thrips or 

 other destructive agencies might be accountable. 



In view of the importance of the matter to alfalfa seed growers, 

 investigations of this subject were undertaken, beginning with the 

 season of 1906. These investigations have been conducted during 

 subsequent seasons at various stations and have resulted in the 

 accumulation of a mass of data which throw new light on the sub- 

 ject. Incidentally they have revealed the fact that the problem 

 is much more complex than had been anticipated, and there is need 

 of much further work, especially in the careful correlation of cH- 

 matic data, as well as the abundance of insects, with the seed yields 

 from season to season. The facts herein set forth substantiate the 

 previous belief in the importance of insect visitors, but also show 

 that, under certain climatic conditions, automatic self-pollination of 

 the flower takes place. The amount of self-poUination varies from 

 season to season and with individual plants. Whether self-pollination 

 is sufficient to produce satisfactory seed yields is stiU a matter of 

 doubt, but the observations at Chinook, Mont., indicate that at that 

 locality this is the most probable explanation. 



Note.— This bulletin deals with the biological problems concerned in the pollinstion and fecundation 

 of the alfalfa flower. It Is intended primarily for technical agronomists and botamsts. 



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