BULLETIN OF THE 
Se) USDEDARTMENT AGRICULTURE « 
No. 75 

Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief. 
April 8, 1914. 
(PROFESSIONAL PAPER.) 
ALFALFA SEED PRODUCTION; POLLINATION 
7 STUDIES. 
By C. V. Pieper, Agrostologist in Charge, and Morean W. Evans, Rotanp McKeg, 
and W. J. Morsz, 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 cli- 
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-pollination varies from 
season to season and with individual plants. Whether self-pollination 
is sufficient to produce satisfactory seed yields is still 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 pollination and fecundation 
of the alfalfa flower. It is intended primarily for technical agronomists and botanists. 
28437°—14——_1 
