212 REPORT OF THE DEPARTMENT OF BOTANY OF THE 
properly belongs to the plant known to botanists as Medicago lupu- 
lina L., but sometimes it has been applied to other plants. Yellow 
trefoil so closely resembles alfalfa as to be easily mistaken for it. 
The most striking difference is in the color of the blossoms, yellow 
irefoil having yellow blossoms while those of alfalfa are bluish or 
purple. When adulterated seed has been used the fraud is not 
detected, usually, until the plants bloom, which is in June of the 
second season after sowing. Yellow trefoil blooms from a week to 
ten days earlier than alfalfa. 
In botanical works Medicago lupulina is sometimes toeecane as 
annual and sometimes as “annual or biennial.” Our observations 
convince us that in New York alfalfa fields it is regularly a biennial 
as announced elsewhere by one of the writers.°? June 4, 1906, the 
writers sowed a tenth-acre plat with alfalfa seed which was heavily 
adulterated with yellow trefoil and two kinds of bur clover (Medi- 
cago hispida and M. arabica). During September of the same year 
some of the trefoil plants blossomed and produced seed, but the 
great majority first began to bloom in the spring of 1907. Some 
blossoms appeared the last week in May and from June 1 on to the 
time of making the first cutting (June 28), the field was yellow with 
bloom. No trefoil appeared in the second or third cutting. Many 
farmers have hal similar experience —the trefoil becomes con- 
spicuous during the forepart of June in the second season after 
sowing and after the first cutting disappears from the field almost 
completely. Even when infested fields are plowed up and reseeded 
the yellow trefoil does not reappear to any great extent. In the 
experiment described above the plants of Medicago hispida flowered 
and produced seed-pods in abundance during the autumn of 1906, 
but Medicago arabica did not bloom and both species were com- 
pletely killed by the winter. 
That plants of yellow trefoil live over winter in alfalfa fields, and 
also in lawns, is further proven by the following experiment: On 
March 29, 1907, nine plants suspected of being Medicago lupulina 
were transplanted into the Station greenhouse. Six of the plants 
were taken from a one-year-old alfalfa field and the other three 
from a well-kept lawn of several years standing. In due course of 
time all nine plants bloomed showing themselves to be yellow trefoil 
as suspected. 
*U. S. Dept. Agr. Farmers’ Bul. 102:33; La. Sta. Bul. 53:40; Mass. Sta. 
Rpt. to (1892): I90. 
"French (33). 
