232 REPORT OF THE DEPARTMENT OF BOTANY OF THE 
have never seen it sufficiently abundant to cause appreciable loss. 
It is usually seen in May and June. 
The cause of white spot is entirely unknown. The affected leaves 
show no evidence of being attacked by fungi and it seems unlikely 
that the trouble is due to insects. It is considerably different from 
the work of the four-lined leaf-bug (Poecilocapsus lineatus) which 
occasionally attacks alfalfa leaves producing small, translucent spots. 
Probably it is a physiological disorder of some kind. The roots 
of affected plants generally appear normal. | 
YELLOW TOP. 
During the past two years one of the Station alfalfa fields, seeded 
in 1904, has turned bright yellow from an unknown cause. In 
1907 this occurred two to three weeks after the second cutting when. 
the plants were seven to nine inches high. It commenced on a strip 
along one side of the field where the hay had been cut a few days 
earlier than on the remainder of the field. Ultimately, an area of 
about two acres became involved. In the spring of 1908 the affected 
field was entirely normal in color and the first cutting of hay was 
a heavy crop; but the second and third cuttings were both very 
yellow and the yield light. This year the trouble started in the 
same place as in 1907 and spread over the entire field of about 
four acres. It also appeared, in a mild form, in two other fields 
on the Station farm. Several fields in the vicinity of Geneva were 
affected and reports of the disease were received from various 
other places in the State. It appears to have been not uncommon 
in 1908. 
On affected plants, the lower leaves are green while the upper 
ones are more or less yellow or, occasionally, purple. As a rule, 
the yellowing is much more pronounced on the distal than on the 
proximal portion of the leaflets. Although the yellow leaves do 
not fall the growth of the plants is severely.checked. 
There is no reason to believe that this disease is caused by any 
fungus, insect or other parasite working in the parts of the plant 
above ground. Plainly, the cause is to be sought underground. Our 
investigation of the roots of affected plants has been too super- 
ficial to warrant positive statements concerning their condition. We 
can only say that from casual observation they appear to be norinal. 
Apparently, climatic conditions have something to do with the 
disease. Dry weather seems to favor it... Both in 1907 and 1908 
it made its appearance during very dry weather. However, alfalfa 
growing in soil containing an excess of moisture frequently shows 
