6 Colorado Experiment Station 
single plants when about six weeks old, thus permitting the study of 
individual plants. 
While the nursery was given uniform cultural care, there were 
marked contrasts in many traits, such as, production of seed; leafiness 
of the plant; coarseness of the stems; degree of resistance to late spring 
frosts, and some other points of practical utility. 
The factor of overcrowding of the plants in the nursery had been 
Plate No. 3.—A portion of the 1907 alfalfa nursery, taken April 25, 1911. 
showing the loss of plants after four winters. In the right foreground, 
a plat of Ecuador alfalfa; in the forground, a plat from Utah seed; in 
the left center, two plats of African alfalfa, all dead, in the right center, 
a plat of Arabian alfalfa, all dead. 
eliminated by thinning the plants to single specimens. Yet after the 
winter of 1907-1908, over one half of the plants in all the plats seeded 
with Arabian and North African seed were dead, apparently from win¬ 
ter killing, while the plats seeded with seed from Spain, Mexico and 
South America had many dead plants and a good many partially killed 
crowns. The same was true in the native American plats. The plants 
were often found with just a few stems with life enough to start 
growth in the spring. But in the Turkestan plats and the plats sown 
with the northern strains of seed, there seemed to be no loss whatever 
from winter-killing. 
During the season of 1908, the nursery was allowed to produce 
