May 6, 1913 YcIIow-Leafblotcli of Alfalfa 309 



direction of the veins. In a few days the blotch may extend from the 

 midrib to the margin if the leaf is small. In shape it remains some- 

 what elongate, as though restricted by the veins. It does not appear 

 that an entire leaflet is ever invaded by a single infection. In color 

 it becomes a deeper yellow, often approaching a brilliant orange on the 

 upper surface, and a little paler beneath. 



Shortly after the appearance of the yellow blotch, sometimes at its 

 first appearance, the central portion of the area shows on the upper 

 surface of the leaf small orange-colored points which indicate the location 

 of pycnidia. They may be very inconspicuous at first. They may be 

 closely grouped along the center of the blotch if it is small, or may be 

 more scattered if it is large. A smaller number of pycnidia usually 

 emerge later on the lower side of the leaf. They soon become deep 

 brown, or even almost black. On mature foliage which has lost its 

 deep-green color, and especially upon plants with narrow leaflets, these 

 elongate groups of dark-colored pycnidia may be the most easily 

 recognized characteristic of the disease. 



The diseased areas may not die and dry out for a long time, especially 

 the foliage may take on a rusty-yellow color with no very distinct lesions, 

 but with pycnidia scattered more or less uniformly over the leaf. Under 

 very dry conditions such leaves may dry out quickly with little change 

 in color. But during protracted rains they quickly become water- 

 soaked and fall off. 



Under very favorable conditions of protracted cool weather, especially 

 in the autumn, these diseased areas may show on the lower surface of 

 the leaf a number of small black bodies which may develop into apothecia 

 before the death of the entire leaf. Ordinarily apothecia do not develop 

 until after the death of the entire leaf (PI. 26). At this time the diseased 

 areas become very dark brown or black in color, in contrast to the light- 

 brown color of that part of the leaf which was not diseased. If the 

 dead leaves remain attached to the plant, they often show a tendency 

 to curl spirally with the lower surface outward. The first apothecia 

 appear as small black dots, rarely as much as a millimeter in diameter, 

 scattered along the diseased areas on the lower surface of the leaf. 

 Later, a few may appear on the upper surface. Occasionally newly 

 infected leaves which have been killed prematurely by frost may develop 

 scattered apothecia which are not located on blackened areas; but if 

 the disease has been at all abundant and the plants have not been cut 

 close too late in the fall, there are usually a sufficient number of dead 

 leaves with characteristic blackened areas present to make possible 

 the recognition of the presence of the disease even during the winter 

 months. 



The disease occurs on stems as well as leaves, but not as abundantly. 

 From field observations it appears that the fungus usually requires a 

 longer time to produce a conspicuous lesion on the stem than on the 



