o 



04 Agricultural Experiment Station, Ithaca, N. Y. 



one part of the leaflet or in another. It may also be stated of the 

 early blight that frequently the leaf tissue situated along the 

 larger veins succumbs to the disease more slowly than do those 

 portions which are further removed from the veins. 



If these diseased areas are very carefully examined, it will be 

 found that it is a very common occurrence to find numbers of 

 slight elevations or ridges arranged in circles about a common 

 center. These may vary slightly in color, but they are perhaps 

 most noticeable on account of their apparent elevation. Since 

 such ridges are absent, so far as my observations go, in areas 

 affected by the late blight, their presence is of considerable value 

 in determining the character of the disease, the more so since the 

 general color of the parts destroyed is very similar in the different 

 cases. 



When the colors of the green and apparently unaffected tissues 

 in the figures are compared, another marked difference will 

 instantly appear. The leaf affected with the late blight shows 

 sound healthy tissues up to the region penetrated by the parasite. 

 The leaflets appear to suffer only in those parts actually invaded 

 by the mycelial threads of the fungus. Yet what is the meaning 

 of the yellow color which pervades almost all parts of the other 

 leaf? Xo parasite appears to have reached these portions, and 

 yet they are manifestly unhealthy. Two explanations might be 

 advanced; first, that the presence of the fungus has an injurious 

 action extending beyond the parts in which it is growing, a 

 supposition which may be said to have but very little support; 

 and second, that the yellow color is due to a natural weakening 

 or maturing of the plant, this in turn being brought about by 

 untoward circumstances or by age. This point will be touched 

 upon more fully under the causes of the early blight. 



In the illustration, the edges of the leaflets are shown as having 

 curled to a very marked degree. Such curling is not necessarily 

 an indication of early blight, since whenever the leaf tissue dies, 

 especially at the outer extremities of the leaflets, the tendency 

 seems to be for the leaf to roll upon itself, as shown in the figure. 

 Yet this character possesses a certain significance. In order that 

 a leaflet should assume the position of those here represented, it 

 is necessarv that the death of the tissue shall occur more or less 



